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Ballistic Characteristics of Wounding Agents
Maj. Ralph W. French, MAC, USA (Ret.), and Brig. Gen. George R. Callender, USA (Ret.)
PHYSICAL ASPECTS OF THE MISSILE CASUALTY
Warfare between individuals or nations to be carried to a successful conclusion requires rendering the enemy noncombatant through injury, or death, and concomitant loss of his ability to function within his assigned duties. In modern warfare, antipersonnel weapons have been developed which are capable of injuring the enemy at a considerable distance from the origin of attack, and means, such as the atomic bomb, have been devised for the wholesale destruction of enemy personnel and materiel. While destruction of materiel plays a role in modern warfare, inflicting injury to cause incapacitation of personnel still remains the most important consideration.
To develop perspective for fair appreciation of modern warfare and its weapons, it is necessary to go back to prehistoric time. It is logical to presume that the earliest warfare was hand-to-hand combat. This was probably quickly augmented by sticks, clubs, or other similar and readily available aids. Following this, prehistoric man no doubt commenced to hurl stones or other missiles easily grasped and thrown. From this stage, it was not too great a step to increasing missile velocity through the aid of the sling, throwing stick, or other means to add to the missile velocity and consequent effectiveness. In brief, man took advantage of the physical law of kinetic energy which remains as the fundamental law in the study of missiles and the formation of wounds.
Considering early history as recorded in the Bible, it is noted that David, in his encounter with the giant, Goliath, was conversant with the advantage to be gained through augmenting his personal strength with small, smooth stones which could be hurled effectively with the sling. This offset the inherent advantage of the giant's strength. It resulted in a missile casualty.
As we come down through recorded military history, we see man aiding his military effectiveness in rendering the enemy hors de combat with the hand-hurled spear or javelin followed by the arrow propelled by the bow or crossbow. In this stage, we see man also adding to his ability by using the horse as a means for increased velocity and force in propelling the spear. However, the arrow was often capable of inflecting injury at greater ranges than possible for hand-to-hand encounter and had excellent ballistic qualities. In this period, there
also was the use of various antimateriel weapons, such as the catapult for throwing stones. Ever since this era, there has been a decrease in the size of the missile and an increase in velocity and consequent range of effectiveness.
With the advent of gunpowder at the battle of Crécy in the 14th century, the potential for greatly increased missile velocities with ability to produce injuries at greater ranges became apparent. However, development was relatively slow, as gunpowder in its earliest applications was often more dangerous to friend than to foe. Metallurgy, chemistry, physics, and the manufacture of weapons had yet to be developed to permit the commonplace applications of modern warfare.
The gunpowder available for many years was dangerous as its rate of transformation into gas could not be accurately controlled and as it also deteriorated on slight provocation. This resulted in many serious disasters through weapon failure. Only with the advent of the so-called smokeless powders could rate of burning be controlled and pressures be held within safe limits.
From the 14th to the 19th centuries was seen the development of small arms through the blunderbuss, musket, and rifle and the development of artillery from the crude wooden cannon to the metal smoothbore and the rifled artillery piece. Smokeless powder with its controllable rate of burning was a 19th century invention. In this period also was seen the use of explosive charges in grenades and landmines, as well as the development of explosive missiles for artillery use.
In the 20th century came the airplane with its potentialities of transporting bombs many miles from the point of origin to inflict injury on enemy personnel and to destroy materiel. There also was marked improvement in powders and other explosive agents.
Analytical retrospection of the entire development of warfare from prehistoric time reveals man's continual struggle to augment his human capability to inflict injury through the utilization of the law of kinetic energy as applied to the moving object. There is a continual trend down through the centuries toward the infliction of injury at even greater distances through increase in missile velocity. In this respect, the airplane is only an agent to carry the missile of destruction to yet greater distances from the point of origin. It results in greatly increased effective battle ranges.
Along with this general trend, it also is noted that an increasingly greater number of people are involved in major military operations with ever-increasing effort toward the development of more and more firepower.
Missile effectiveness has been observed to be a function of velocity, and, in keeping with this, it was but natural that through the ages there has been a continual increase in missile speeds. Before the advent of gunpowder, missile velocities at best could not exceed several hundred feet per second. From the 14th to the beginning of the 20th century, missile velocities were increased to approximately 2,000 f.p.s. (feet per second). In the period 1900-1918, velocities were again increased up to approximately 4,000 f.p.s. From that
date to 1953, and taking the atomic bomb into consideration, missile velocities have been increased to approximately 20,000 miles a second. No doubt some of the radiation components of the atomic bomb have greater velocities than this. However, gunpowder and its related agents were responsible only for a velocity increase to something more than 7,000 f.p.s., the greater increase being due solely to the nature of atomic fission and its reactions.
Progressively, the outstanding steps in this analysis of missile warfare and its development down through time follow: Clubs, stones, sling, bow to propel an arrow, gunpowder, rifle, smokeless powder, TNT and related propellants, airplane, rockets and rocket-propelled bombs, and the atomic bomb.
From this brief résumé of the progressive development of the missile as an antipersonnel agent, it is natural to inquire just how that missile produces a casualty. While medical men have served with the armies for many years, it was only recently that studies to determine the mechanics of wound production have been instituted. There has been some observation and many reports but little organized research, mainly because available instrumentation was inadequate for a serious, comprehensive study.
Better appreciation of the detailed mechanics of wound production has a dual purpose. First, a more complete knowledge of the wound and its extent permits better definitive treatment by the military surgeon; second, this knowledge permits the design of ordnance materiel for antipersonnel purposes on scientific grounds. It also lessens the need for costly rule-of-thumb or "cut and try" methods by either the military surgeon or the ordnance engineer.
It is the purpose of this chapter to bring together the salient principles regarding the missile casualty as a physical entity, a cause and effect phenomenon. These principles explain many apparent anomalies as seen by the surgeon unacquainted with the detailed mechanics of wound formation and may aid the ordnance engineer in his design problems.
Frequently, the military surgeon has seen small entrance and exit holes in the skin of a gunshot casualty and taken it for granted that the internal damage was correspondingly small. Had he known more of the modern high-velocity rifle bullet and what is known as yaw, the trivial external wounds would not have misled him in his initial treatment of the wound. Also, had he been appreciative of the true magnitude of the forces involved, his mental picture of the wound would have been far more accurate.
For many years, the ordnance designer gaged the effectiveness of missiles by their ability to penetrate pine boards or similar materials. However, when an accidental discharge of a shrapnel round raised a serious doubt as to the real value of shrapnel as an antipersonnel agent, this rule-of-thumb gage was found to be valueless as a criterion. The ordnance designer wanted some "real" information from the medical man of what was necessary to produce a casualty.
For the sake of a comparable yardstick in evaluation of ordnance materiel, a missile with 58 ft.-lb. (foot pounds) of kinetic energy was considered to be capable of producing a casualty. While this has not been fully substantiated
as a fair criterion, it is well supported1 and is definitely superior to pine boards. No doubt, under optimal conditions, a missile with considerably less energy than 58 ft.-lb. can produce a serious wound, but on the average it is probable that this amount of energy will insure a casualty.
Though much has been accomplished in a comparatively short time in explaining many of the factors entering into the physical formation of the wound, much remains to be learned. There is the question of how the yawing rifle bullet produces such damaging injuries. There also is the question of nerve injuries-their cause, extent, and repair. Again, just how much debridement is necessary to insure repair? These are but a few of the physical, physiological, and pathological problems yet to be answered.
The Missile Source2
Small arms.-In considering the missile casualty, small arms naturally fall into several classifications based on the character of wound. For the purpose of this discussion, small arms will be considered as those weapons so classified by the Office of the Chief of Ordnance, U.S. Army, with a caliber of approximately 0.60 inch or less.
Sidearms.-These are small weapons designed primarily for personal defense. In World War II, some automatic weapons in this category also were designed for effective offensive employment at near ranges. Muzzle velocities ranged from a little more than 800 f.p.s. for the U.S. sidearms up to nearly 1,200 f.p.s. for those used by the Germans. The comparatively low velocities produced minimal wounds.
Carbine.-In the U.S. Army, the .45 caliber pistol was often replaced by a .30 caliber carbine firing a 110-grain bullet with a muzzle velocity of 1,975 feet per second. This was a semiautomatic weapon useful for offensive as well as defensive action. It also was used by paratroopers and others requiring a small, effective weapon. While essentially a shoulder weapon, the ballistic characteristics placed it more in the category of a super sidearm, and missile casualties from this weapon were more of the sidearm type.
Shoulder weapons.-The basic offensive weapon of the foot soldier is the shoulder weapon. From the lessons learned in World War I, the trend in military weapons has been toward the development of semiautomatic arms to relieve the soldier of the interruption due to loading the weapon. Consequently, there has been an increase in the rate of aimed fire and firepower. However, many repeating rifles of the older magazine type were used in World War II. From the missile-casualty standpoint, the most important consider-
ation is the muzzle velocity of the shoulder weapon projectile, as this largely determines the effective range and the type of wound. In World War II, the muzzle velocities of the Japanese rifles ranged from 2,200 to 2,400 f.p.s.; of the German rifles, from 2,500 to 2,700 f.p.s.; and the muzzle velocities of some of the U.S. shoulder rifles were slightly more than 2,800 f.p.s. In general, at combat ranges, comparatively severe wounds are to be expected from any of these weapons, much more so than the wound produced with the usual sidearms missile and velocity.
Machineguns.-In the machinegun category are the antipersonnel full automatic weapons using essentially the same ammunition as the shoulder weapons of corresponding caliber. Weapons of this type in the larger calibers are primarily antimateriel agents and will be considered later in their secondary antipersonnel aspect. As a missile-casualty agent, machineguns are essentially the same as shoulder weapons except for one important factor. Full automatic weapons fire at a high cyclic rate, 400-800 rounds a minute. This commonly results in multiple wounds, all of a severity to be expected with the shoulder weapon missile. This also accounts for the fact that the machinegun missiles proportionately produce a greater number of fatal casualties.
Automatic weapons larger than 8 mm. (0.315 in.).-While classed as small arms, weapons in this category (most of them 0.50 inch in caliber) are designed primarily for aircraft, AA (antiaircraft), and antimateriel purposes. The larger size of projectile permits the practical use of an HE (high explosive) bullet as well as other types of missiles designed for specific purposes. While some wounds are certain to be caused by these missiles, the casualty is usually incidental to the use of the weapon for other missions.
Antitank small arms.-The Germans had three types of 7.92 mm. (0.312 in.) nonautomatic AT (antitank) guns of interest. One, an ex-Polish model, had a muzzle velocity of 4,100 f.p.s., while the other two had muzzle velocities of 3,540 f.p.s. Early in World War II, these weapons were quite effective and were capable of penetrating more than an inch of armor at a range of 100 yards. However, with the increase of tank armor protection, they lost their value and became effective only against light-armored vehicles. The high-muzzle velocities are of interest, though it is unlikely that many missile casualties can be ascribed to these weapons.
Ammunition.-For sidearms and shoulder weapons, ball-type ammunition is generally employed. This usually consists of a lead core protected with a jacket of gilding metal or similar material. Most bullets in military use are sharp pointed, having the so-called spitzer nose. Some have a flat base while others are boattailed. Some medium-velocity ball ammunition is used with the carbines or other special defensive weapons.
Small arms ammunition commonly used with machineguns and aircraft and AA weapons in the small arms category includes:
While casualties may occur with any or all of these various types of bullets, other than ball, the primary use of these bullets is for other purposes. Most of the varied types of ammunition find their greatest use in aircraft and AA work. However, under certain ground conditions, tracer, incendiary, and AP (armor-piercing) types are of value in machinegun missions.
Wounds resulting from tracer, incendiary, or HE bullets are complicated by various effects peculiar to the particular missile. Tracer and incendiary bullets not only introduce the factors peculiar to their chemical characteristics but usually produce severe wounds because of their comparative lack of stability, their low cohesiveness, and their poor ballistic characteristics resulting from loss of mass. They often yaw badly and break up on impact. Wounds often suggest the use of explosive bullets. While international agreement had prescribed the HE missile for small arms use, the Japanese had such bullets for their 7.7 and 12.7 mm. weapons, presumably for use in aircraft and AA weapons. However, in view of the fact that aircraft often strafed personnel, the complaint regarding wounds from HE bullets was logical.
Japanese 6.5 mm. bullet with enlarged core in the base.-In correspondence,3 it was suggested that this bullet was probably launched at velocities higher than those usually credited to the Japanese 6.5 mm. ammunition. This was believed erroneous because of the weight of the bullet. The 6.5 mm. rifle was a comparatively old gun, and no doubt materials inferior to those available in modern weapons had been used in its construction. It also was not designed for chamber pressures common in more modern weapons. The bullet weighed 138 grains (figs. 45 and 46) and was homologous with a 161-grain .30 caliber bullet. A bullet homologous with the 150-grain .30 caliber bullet would weigh 129 grains.
Knowing the chamber pressures necessary to launch a 161-grain bullet in the .30 caliber rifle with a velocity comparable to the 150-grain bullet, it was logical to presume that the Japanese fired this bullet at a muzzle velocity of 2,300-2,400 f.p.s., usually credited to their standard 137.3-grain bullet.
However, the spin imparted to the bullet by the rifling would have a negligible effect in effecting stabilization in denser mediums, such as tissues. In fact, the increased mass in the tail of the bullet would undoubtedly operate to increase greatly the degree of yaw on entering a dense medium. This bullet would probably have slightly less stability in air than one of a more conventional design, so that the degree of yaw on impact would normally be somewhat larger also.
FIGURE 45.-Japanese 6.5 mm. (0.256 in.) bullet with odd-shaped core of antimony lead mixture. Shape of core changed dynamic characteristics of the bullet so that it was apt to cause severe wounds at near range because of excessive yaw. Weight of the bullet was 138 grains. (Magnification three times actual size.)
FIGURE 46.-Japanese bullets with peculiar core recovered after being fired into water. To the left is a U.S. M1 bullet fired and recovered in the same manner for comparison. The Japanese bullets deformed at the base as is commonly noted with military full metal patch bullets with the spitzer nose on impact at velocities in excess of 2,000 f.p.s. It was also noted that the core separated from the jacket in two cases. This last was also noted in wounds produced by this Japanese bullet in jungle fighting at near ranges.
In general, it has been observed that with sufficient velocity all cored metal-jacketed bullets will break up or deform on impact. The most resistant to disintegration is the sharp-pointed spitzer bullet. However, at close ranges and impact velocities in excess of 2,400 f.p.s., this bullet often shows deformation, with breakup appearing first in the base of the bullet. On the other hand, the round-nosed bullets break up at velocities from 1 to 2 thousand feet less, but their first deformation occurs at the nose. Bullet breakup or deformation of the full metal patch missile is most apt to occur on impact with hard bone.
Soft-nose hunting-type bullets break up at lower velocities and often commence to disintegrate in the skin immediately after impact. Fragments of jacket and lead core are found in quite superficial tissues when impact velocities are excessively high-2,200 f.p.s. or more.
Projectile, artillery.-Although in all wars before World War II various antipersonnel loads such as canister, grapeshot, chain shot, and shrapnel were used, experience had conclusively demonstrated the comparative ineffectiveness of these agents for antipersonnel purposes. The HE projectile, however, had proved to be not only more effective in producing casualties but had also proved capable at the same time of inflicting materiel damage which is often of greater importance in carrying out the artillery mission.
The HE projectile is capable not only of penetrating an earthwork but, after the penetration, of detonating and producing casualties in the personnel, supposedly protected by the earthwork, by the many high-velocity fragments resulting from the detonation. Various types of contact, delayed action, and time fuzes permit almost uncanny timing of projectile detonation.
Ineffectiveness of the special antipersonnel cannon loads has been due in the past to the comparatively low projectile velocities at battle ranges. Though this was not so apparent at the battle ranges common to warfare before the 20th century, it became a certainty with the experiences of World War I. The advent of smokeless powder, better types of steel, and manufacturing improvements made practicable increased artillery muzzle velocities, but these factors did not materially increase the effective remaining projectile velocities. The battle ranges increased commensurately with the increase in muzzle velocities so that remaining velocities remained essentially constant.
On the other hand, fragments resulting from the detonation of HE projectiles have increased materially in effectiveness as antipersonnel agents. Control of burst has been much improved through more accurate fuzing. Initial fragment velocities have been more than doubled (from less than 3,000 to more than 6,000 f.p.s.) by the utilization of new explosives. Fragmentation has been controlled also through improved projectile design and through the selection of better fragmenting materials in construction.
High-explosive detonation charges have resulted in a much greater number of effective fragments than was possible with the other types of antipersonnel projectiles. For instance, the total number of balls in a 3-inch shrapnel load was less than 300 compared to the thousand-odd effective fragments from a 75 mm. HE shell at 20 feet from the point of burst. The 81 mm. HE shell with an initial fragment velocity of 6,180 f.p.s. has more than 2,500 effective fragments at a distance of 20 feet from the point of burst. The fragment distribution from HE projectiles also covers a greater area than shrapnel balls.
Casualties resulting from high velocity HE fragments sustain more severe wounds than do those resulting from the relatively low velocity shrapnel balls. In fact, shrapnel velocities were often so low that neither clothing nor skin penetration was effected within a few yards of the burst.
Though the application came in the latter part of World War II, the use of the radar proximity fuze materially enhanced the value of the HE projectile as an antipersonnel weapon. It insured the burst's occurring under optimum conditions for casualty production. This development undoubtedly points the way to the HE projectile's being used much more in the future as a specific antipersonnel weapon. Somewhat similar effects were noted in jungle warfare when fuzed projectiles were detonated by contact with the trees. In effect, this resulted in an airburst under optimum conditions.
A canister projectile was used in the 37 mm. gun at close ranges against tank personnel. The canister was loaded with 122 lead balls weighing approximately 100 grains each. Velocity was imparted to the balls by the 2,500 f.p.s. muzzle velocity of the canister. This load could only be effective at pointblank ranges where remaining velocities would be adequate. The canister was designed to release the balls immediately on firing, so rapid retardation of the balls could be anticipated because of the lack of desirable ballistic characteristics.
In artillery work, the only other projectiles usually used were the shot or AP loads and various chemical loads, such as flare and smoke. These loads have little significance as antipersonnel agents, casualties only being incidental to their primary purpose. Of course, some casualties result from direct hits by AP projectiles as well as by the secondary missiles resulting from their impact. In some phases of tank warfare, both can be major causes of tank casualties. Both also may be significant in naval warfare.
The Japanese still used some shrapnel of conventional design with their 75, 105, and 150 mm. guns. At near ranges in jungle fighting, shrapnel could have greater antipersonnel value as the remaining projectile velocity added to the initial velocity imparted to the shrapnel balls by the black powder bursting charge could make the balls effective missiles for a short distance. However, the usual muzzle velocity of Japanese artillery was low as compared with that common to modern weapons. It is apparent that the Japanese were either not cognizant of the value of velocity or were unable to produce weapons capable of sustaining the higher powder pressures necessary to secure the increased muzzle velocities.
The Germans had an interesting and effective antipersonnel 8 cm. HE mortar shell known as the "Bouncing Betty." On impact, a nondelay fuze ignited a smokeless powder charge which in turn ignited a delay pellet. The explosion of the smokeless powder charge sheared off pins holding the nose cap to the projectile body and threw the shell from 5 to 10 feet into the air. In the meantime, through the action of the delay pellet and a booster charge, the main TNT bursting charge was detonated at approximately the moment the projectile was at the height of its bounce. This was a simple means to obtain the effect of an airburst. Initial fragment velocities with TNT of approximately 3,500-4,000 f.p.s. resulted in effective fragment distribution for a considerable range.
Though World War I saw the first application of the airplane to warfare, it remained for World War II to demonstrate its use as a formidable military weapon. Personnel were attacked in one of two ways: By gunfire in strafing or by aerial bombs.
Missile casualties due to strafing have characteristics typical of small arms injuries except for several possible details. The speed of the airplane can add to wound severity by augmenting the bullet velocity by as much as 800 feet per second. Some casualties may also be due to tracer, AP, explosive, or other special bullets commonly used in airplane weapons. Another important factor is excessive yaw, as many gun barrels are in such a condition that the bullets are not stabilized. In rapid fire, the generated heat also expands the barrel to such an extent that the bullet may not follow the rifling.
Peculiar to the airplane as an antipersonnel weapon is the aerial bomb. While bombs are used for many other purposes, the fragmentation bombs are designed particularly for antipersonnel use. They are so constructed that on detonation there will be a spray of effective fragments capable of producing casualties over a considerable area. These antipersonnel bombs come in several sizes, ranging in weight from 20 to 260 pounds each.
Fragmentation bombs are somewhat similar to HE projectiles in that the bursting charge constitutes approximately 10 percent of the weight of the bomb. However, the bomb is specially constructed to yield a greater number of effective fragments. Fragment size is roughly controlled by design and construction.
At 100 feet from the point of burst, the 20-pound fragmentation bomb averages 829 effective fragments; the 90-pound bomb, 2,880; and the 260-pound bomb, 5,450 effective fragments. Because of the bomb design and the ratio of bursting charge to bomb weight, fragments are fairly large and at 100 feet from the point of burst have velocities of a little more than 1,000 feet per second.
The smaller 20-pound fragmentation bombs are commonly dropped in clusters of six bombs so that a salvo effect is obtained. A single plane may simultaneously drop a number of clusters. Planes in a group may drop their bombs all at about the same time, so that a considerable area can be blanketed with effective fragments. Many casualties are certain to result among exposed personnel. Small bombs dropped simultaneously in groups are more effective than a single bomb of the same weight.
Other bombs, though not designated for antipersonnel purposes, can cause missile casualties. The general-purpose type, usually with a bursting charge approximately one-half of the bomb's weight, is often used under conditions in which personnel will be exposed. As an example of performance, the 100-pound general-purpose bomb has 3,310 effective fragments at a distance of 100 feet from the burst moving at a velocity of 1,870 feet per second. The higher velocity makes fragments of a smaller size more effective than would be true
with the fragmentation bomb. However, this bomb has a much greater blast effect and depends largely on that effect in accomplishing its primary mission.
In some of the very large light-case bombs, the detonating charge accounts for 75 percent of the bomb's weight. These bombs, designed particularly for demolition work, accomplish their mission almost entirely through the blast effect. There also are other special-purpose bombs, such as AP, flare, and flashlight. The Germans had an AP bomb which was equipped with auxiliary rocket propulsion to give acceleration to aid in penetration.
Fragment distribution from a bombburst is fairly symmetrical with respect to the longitudinal axis. When a bomb drops with its axis vertical and detonates on contact, fragments fly in all directions. However, most bombs actually fall with their axis at such an angle to the perpendicular that there is considerable asymmetry in actual fragment distribution. The most dangerous sector is that from which the bomb's axis is leaning on detonation. On the opposite side from the burst, effective fragment range is much less.
Bomb detonation is effected through the action of a fuze which is armed when the bomb is dropped from a plane or shortly thereafter by the action of a wind vane. Fuzes are of two basic types-instantaneous contact or delayed action. Delay may be a small fraction of a second, or it may be some definite longer interval. Time fuzes similar to those used with artillery projectiles are only used with aerial bombs carrying flares or flash powder for night photography. It has not been practical to initiate airbursts through the use of time fuzes as time of flight is not sufficiently constant.
Though contact fuzes are designed to function instantaneously, there is, in fact, some time lapse between initiation of the primer and detonation of the bursting charge. In this interval, a bomb may penetrate the earth to such an extent that much of the force of the explosion is expended against the earth and upward. The earth acts in a degree to protect personnel. In the case of firm or impacted earth, the bomb may also disintergrate on impact so as to fail to function.
Obviously, for antipersonnel purposes, optimum results can only be expected from an accurately controlled airburst over exposed personnel. Application of the proximity fuze to the aerial bomb may accomplish this. However, in World War II, the most effective antipersonnel bomb was either the properly designed fragmentation-type or the general-purpose bomb, each neither so large nor so heavy that dampening earth penetration would occur before detonation. Under some conditions, small bombs lowered by parachutes to delay the descent were found to be particularly effective as antipersonnel weapons against personnel in the open or in foxholes.
Hand and Rifle Grenades
Most hand grenades are primarily offensive weapons of the fragmentation type. Some have fairly thick cast iron walls divided into serrated segments and others have comparatively thin steel casings. The Germans used one
offensive hand grenade which consisted of a pressed disk of explosive RDX (cyclonite) and wax with a fuze inserted in a hole in the side of the disk. This grenade depended on blast effect alone for performance.
One of the cast iron, fragmentation-type hand grenades loaded with TNT as a bursting charge had 254 effective fragments with an impact velocity of nearly 2,000 f.p.s. at 20 feet from the point of burst. Many of the fragments had sharp, serrated edges and at impact velocities of nearly 2,000 f.p.s. would produce severe wounds. However, velocity was rapidly retarded so that effective range was not great.
Grenades are of various shapes, some for direct throwing, while others of the so-called potato-masher type have a wooden handle to aid in hurling. Rifle grenades are similar to hand grenades, except that they are launched by means of a rifle and consequently have greater range. Some special grenades, hand and rifle, of the AP hollow-charge type were developed for AT use. Their value as missile-casualty agents is quite secondary.
Grenades can only be thrown or propelled to a limited range, so usefulness is restricted to certain conditions. While the range must be such as not to endanger friendly troops with resultant fragments, it also must permit of reasonably accurate throwing. Grenades are particularly effective when tossed into a pillbox or thrown into an occupied dugout. In World War I, hand grenades were especially useful in clearing trench bays. When fragmentation grenades detonated in close groups of personnel, casualties with severe, multiple wounds resulted.
The Japanese had a hand grenade made of terra cotta. It was charged with 3½ ounces of explosive which would burst the terra cotta container into fragments dangerous at near ranges. Many of the Japanese grenades were odd, in that the fuze mechanism had to be armed by a sharp blow before hurling. After arming, there was a 4- to 5-second delay pending detonation.
Many hand grenades were used for the preparation of boobytraps. Once armed, grenades are sensitive and make a dangerous boobytrap which cannot be easily unarmed. Severe wounds can be expected, as the victim is usually close to the explosion, where many high-velocity fragments and secondary missiles will be the rule.
Landmines are of two categories-AT and antipersonnel. The former usually requires so much weight to initiate the primer that it is of little direct interest as a casualty-producing agent. On the other hand, the sensitively fuzed antipersonnel mine is highly effective and is often responsible for many and severe casualties.
Basically, the landmine is a defensive or protective weapon, hence more likely to inflict casualties on an advancing force. The antipersonnel mine also quickly exacts its toll of the careless or inexperienced soldier. It may be
equally dangerous to friend or foe, especially when the soldier is careless and disregards warning signs of a minefield intended to protect a bivouac or beachhead.
Mines commonly inflict severe wounds as the victim is usually very close to the detonation, often standing directly over the mine. Many lower extremity casualties can be expected. When individuals are advancing in close formation, a single mine can be responsible for multiple, severe casualties. Many mines not only have a considerable immediate range but often are so sensitive as to be detonated by neighboring detonations, so that the tripping of a single mine may fire one or more in the near vicinity.
Though landmines of various types have been used in warfare almost since the inception of gunpowder, before World War I they were crude improvisations. Most were comparatively ineffective. In World War I, the tank and armored vehicle on one hand and the hand grenade on the other hand naturally led to the development of the boobytrap and antivehicle and antipersonnel mine. This development was greatly favored through the use of TNT, a powerful but at the same time a comparatively safe explosive to handle.
Modern production methods as well as modern explosives made wholesale use of landmines both practicable and effective in World War II. Boobytrapping was developed to a new high, with grenades or antipersonnel mines commonly providing the effective part of the boobytrap. Any soldier could handle deadly TNT with impunity until it was set in place and sensitively fuzed.
Antipersonnel landmines commonly carry a charge of a pound or less of TNT or similar explosive and are generally no more than 4 to 5 inches in their greatest dimension. They may be detonated by the direct pressure of 15 to 40 pounds or by a few pounds pull on an apparently innocuous trip wire. Early in the war, mines usually were in metallic containers, but with the development of magnetic mine detectors many were made of glass, earthenware, or plastic to prevent detection.
Early types depended on the fragmentation of the mine container and component parts together with secondary missiles of sand, pebbles, and dirt for their effectiveness. Later, mines were developed which bounced from 6 to 7 feet into the air before the main detonation occurred, thereby effecting an airburst making the fragmentation effective over a much greater area. The Germans developed several mines of this type which also carried shrapnel balls to add to the missiles of normal casing fragmentation. One of these mines had 350 steel balls weighing approximately 53 grains each. This shrapnel filling propelled by 8 to 16 ounces of TNT had an effective range of 150 to 200 yards. There also was a very effective wooden box German antipersonnel mine which did not activate the magnetic mine detectors. This mine was simple and cheap to construct. It also was constructed in a larger size for AT use.
The hot gases ejected by a detonating bomb sweep out and compress the surrounding air and throw that compressed body of air against adjacent layers of air. In this way, a belt is formed within which the air has high pressure and high outward velocity. This belt is limited by an extremely sharp front (less than one-thousandth of an inch) called the shock front in which the pressure rises abruptly.
The shock front travels away from the point of detonation with an extremely high initial velocity (3,000 f.p.s. at 60 feet from a 4,000-pound light-case bomb where the pressure jump is 100 pounds per square inch). The velocity then decreases rapidly towards the velocity of sound (about 1,100 f.p.s.) as the shock front travels on and the pressure jump decreases.
For a better appreciation of the comparable velocity of the blast wave, it is well to consider some of the better-recognized air velocities encountered in winds and storms. Winds of 50-60 miles per hour are classified as gales, and in hurricanes wind velocities of 80 miles per hour are common with now and then velocities in excess of 100 miles an hour being reported. Wind velocities in tornadoes have not been accurately recorded but are judged to be of the order of 200-300 miles per hour. The fact that tornadic winds often blow straws into tree trunks is well established in weather bureau documents. The highest wind recorded by a weather bureau was slightly more than 230 miles an hour at the top of Mount Washington, N.H. Though the blast wave travels at a velocity of 4,000 f.p.s. or more when initiated, it quickly damps down to the velocity of sound in air. This is approximately 1,100 f.p.s., the equivalent of 750 miles per hour. It is due only to their very short duration that blast waves are not far more destructive than they are in fact.
The excess pressure prevailing at a point in the air after the arrival of the shock front decreases and vanishes in a short time (about 0.04 second at 400 feet from a 4,000-pound light-case bomb; about 0.006 second at 50 feet from a 100-pound general-purpose bomb) and is followed by minor disturbances which often include a partial vacuum. The entire disturbance produced in air by the detonation of a bomb is called blast.
Peak pressure.-The peak pressure-the highest excess pressure which is attained right at the shock front-gives a measurement of the maximum force exerted against a structure by the blast (pressure X area = force).
Effects of confinements.-The presence of obstacles which prevent the travel of blast in some directions may increase the effect of blast in other directions.
A blast traveling along a tunnel, a corridor, a trench, and, in the case of large bombs, even along a street is effectively confined, so that its intensity decreases much more slowly than in the open.
When a bomb detonates inside a house, demolition of the walls may occur even if the distance from the point of detonation to the walls exceeds the
radius of damage for the same type of bomb bursting in the open. This is due to a variety of effects, among which is the "multiple punch" effect created by the blasts' hitting on a wall in quick succession after having been reflected by other walls. If the effect of blast is intensified on one side of a wall by its confining action, it is reduced by the same token on the opposite side of the wall by its screening action.
Protection from blast.-A wall effectively reduces blast pressure and impulses on objects close to it if it is about 10 feet by 10 feet or larger and if it is of sufficient strength to withstand the blast.
Foxholes, slit trenches, or ditches reduce the blast pressure by about 50 percent. A system of four right angles reduces it to about 15 percent.
Position of the body can have a considerable influence in protection from blast effects. Lying prone on the ground will often materially lessen direct blast effects because of the protective defilade effects of irregularities in the ground surface. Ground also tends to deflect some of the blast forces upward. Standing close to a wall, even on the side from which the blast is coming, also lessens some of the effect.
Many of the persons said to have been injured by blast were actually injured through the secondary effect of being knocked down and forcibly coming in contact with the earth or with other hard objects. If the head of a person thrown down comes in contact with a stone or similar hard object, injury may be quite severe. Any lessening of the distance through which one falls will lessen the probable degree of injury.
Orientation of the body also affects severity of the effect of blast. Anterior exposure of the body may result in lung injury, lateral position may result in more damage to one ear than the other, while minimal effects are to be anticipated with the posterior surface of the body toward the source of the blast. Defilade and reflection of the blast from the body itself may have some effect.
Blast pressure and the orientation of an object.-At a distance of 20 feet from the point of detonation, the peak pressure on a wall parallel to the direction of travel of the blast wave is only about one-seventh of the pressure measured on a similar wall placed at right angles to the direction of travel of the blast. This factor varies with distance, and at 200 feet from the point of detonation the ratio is about 1:2. Pressures on oblique surfaces vary accordingly.
The effects of peak pressures (table 18) follow:
At peak pressures of 500 pounds to the square inch, 50 percent killed.
At peak pressures of from 60 to 100 pounds to the square inch, 50 percent seriously injured.
At peak pressures of 15 pounds to the square inch, eardrums ruptured.
At the nearest point, peak pressures would be between seven and eight times greater on an object oriented at right angles to the travel of the shock wave; at a distance of 90 feet, the factor would be approximately four; and at 150 feet, about three.
TABLE 18.-Peak pressures in pounds per square inch at varying distances from point of detonation for general-purpose bombs of various weights on a surface parallel to direction of travel of shock wave
Blast alone may cause serious injury or death at distances from 120 feet for the 4,000-pound light-case bomb to less than 60 feet for the 100-pound general-purpose bomb. However, it also is more than likely that with within such ranges bomb fragments or secondary missiles will be responsible for injury.
For this discussion, a secondary missile will be considered to be a missile which has been set into motion by another or primary missile and which has traveled for an appreciable distance in the air or more mediums before causing a casualty. This eliminates body-armor fragments, pieces of clothing, and other articles on the person from consideration as secondary missiles at this time. Fragments of bone or other tissues may be secondary missiles under certain conditions.
Many wounds are produced by secondary missiles given their velocity by the blast of the primary bomb, mine, or projectile. Bullets may strike dry sand, rock, or other material which may be moved or broken and thereby set into motion secondary missiles capable of producing a wound. Such wounds may be comparatively trivial but painful and may be fully capable of rendering a man a noncombatant for some time. A face peppered with sand can be quite bloody and painful, though actual injury is but skin deep.
Secondary missiles probably produce more casualties than all other causes combined in the aerial bombing of the unprotected civilian city habitations. Flying glass is particularly bad, even at a considerable distance from the source of the blast. Two factors make glass particularly bad: First, it is easily broken; and, second, the fragments are usually of a shape and type which will readily penetrate the flesh.
The landmine probably attains its maximum antipersonnel qualities from the many high-velocity secondary missiles of sand, dirt fragments, and other materials immediately over the mine. The way it is planted and detonated
is designed to make the most of the secondary missile as a casualty-producing agent. High-velocity propellents are commonly used in mines; the case holding the propellent is comparatively light; and the detonation occurs close to the victim, often within a few inches or at most only a foot or so. Impact velocities are certain to be high.
Light secondary missiles may have high velocities, approaching the maximum possible with any given propellent. Heavier missiles have correspondingly lower velocities. Under certain conditions, for instance, a rifle bullet can spall out a fragment of armor and in so doing impart to the spall a velocity greater than 50 percent of the bullet's impact velocity. Such a spall may produce a more serious wound than the original bullet, because of its size and sharp, irregular edges.
In the immediate vicinity of a bomb or shell detonation, large objects, such as bricks and stones, may be set in motion as secondary missiles. Initial velocities as a rule are not so great, but their greater mass gives them a considerable danger range. Lighter fragments lose velocity more rapidly.
When metal objects, such as nails, screws, and nuts, are set in motion as secondary missiles, they can produce serious wounds. Such objects have been used in artillery projectiles as well as in the older types of landmines (fougasse). Retardation is a function of sectional density (A/M) (p. 121) and, in general, the greater the density of material the longer it will remain dangerous because of impact velocity.
Secondary missiles may be important also in connection with the detonation of HE artillery projectiles, though normally not to the same degree as in the case of aerial bombs, as the detonating charge is comparatively smaller. The projectile design also favors the production of projectile fragments, which generally range farther and are a much more potent factor as a casualty producer than the secondary missile.
Probability of a Missile Casualty
From time to time, the ordnance engineer asks the military surgeon for an opinion on the probable effectiveness of a proposed antipersonnel agent in producing effective casualties. The ordnance engineer is also seeking a mathematical expression which will permit a calculation of the probable effectiveness of a given antipersonnel agent.
The designer of a shell or bomb can usually predetermine the probable fragment size, velocity, and average distribution. He has also adopted an arbitrary criterion of 58 ft.-lb. of kinetic energy as determining a fragment which is capable of producing a casualty. However, he lacks mathematical information as to human body vulnerability and is commonly unable to predicate very accurately the battlefield performance of a given agent.
Some research and analysis has been attempted to bridge this important gap of equal interest to the ordnance designer and military surgeon. So far, the arbitrary criterion of 58 ft.-lb. of energy for an effective wound-producing
missile has proved to be reasonable. It provides a basis upon which the relative effectiveness of antipersonnel agents may be compared.
Before absolute predictions are possible, however, much more must be known about the target. What is the target area? What proportion of that area is actually incapacitatingly vulnerable to an effective missile?
Target area is variable due to body presentation. Black, Burns, and Zuckerman,6 in England, calculated the average projected area of the full standing figure as follows:
This projected area can vary and can be reduced to a much smaller amount as the figure turns sidewise, kneels, or lies prone. The kneeling position presents approximately 55 percent of the full figure, sidewise some 45-50 percent, and the end-on prone figure less than 25 percent of the full figure.
After determining the area of presentation, the question of incapacitating vulnerability must be determined, as many wounds in the total body area will not necessarily incapacitate a soldier. There is some difference of opinion as to the proportion of this incapacitating vulnerable area. Zukerman and coworkers considered that some 10 to 15 percent of the projected area represented the projection of vital organs. They also concluded that the effective vulnerable area to small high-velocity fragments was 2.83 square feet or 67 percent of the total area. McMillen and Gregg,7 in an independent approach to the problem through anatomical analysis, found the projected incapacitating vulnerable area of the full, standing figure as follows:
Relative percent of vulnerable area also varies to a marked degree with the position of the figure. For instance, in the prone figure, head on toward the missile source, at least 75 percent of the presented area is vulnerable.
Another potent variable is the angle of incidence of the missile with respect to the target area. For instance, a missile striking the thorax at a low angle of incidence will often produce a superficial wound, while one striking more nearly at a right angle to the target will penetrate and produce a severe wound or fatal casualty. The first may not immediately materially impair the soldier's fighting ability nor require any prolonged hospitalization or treatment. The severe wound could, on the other hand, permanently remove the soldier from the fighting forces.
While the extremities account for less than one-third of the projected vulnerable area, casualty statistics commonly ascribe well over one-half of the casualties and resultant time lost to the service to extremity injuries. This in part is attributed to the fact that fractures are more common in the extremities and that fractures are injuries which definitely require immediate as well as prolonged treatment.
This apparent bias in wound distribution may be influenced by several factors. First, available casualty statistics are based on a study of the wounded rather than the wounded and the killed. It is well established that much data based on the killed are quite erroneous.
Another variable and unknown factor which could materially affect casualty statistics interpreted on the premise of random distribution of missiles is the degree of earth penetration effected by a projectile or bomb before detonation. Any penetration will result in some defilade effect and in turn affect the purely random distribution of fragments. There usually is some penetration and in soft earth it may be considerable before the bursting charge actually functions. Where there is penetration, fragments are naturally deflected upward by the earth surrounding the projectile. This results in some increase in fragment density in the lower zones, while the earth surface will be protected from fragments by the defilade effect of the earth immediately surrounding the projectile.
Personnel in the immediate vicinity of the burst will be subjected to a shower of high-velocity fragments from the knee level up. Many fragments will be capable of producing severe wounds. Those hitting the extremities will often cause severe fractures, while the same fragment striking a vital area in the soft tissues will frequently result in a fatality. In general, extremity injuries are not so fatal as those in the body or head areas.
Study of detailed statistics supports this approach to the problem of apparent bias in casualty statistics. There is an increasing number of fractures upward from the ground-more in the upper than in the lower extremities, though the area of presentation of the upper is less than that of the lower extremities. Fractures below the knee are definitely fewer than those above that point, indicating a fairly definite defilade effect as just predicated.
Though there would often be fractures in the case of the killed in action, it is known that only too often the statistical studies fail to record them with the cause of death being ascribed to another more apparently fatal effect.
Another factor in World War I fighting which could have materially influenced the wound distribution and statistical studies was the machinegun. In many sectors, it was the practice to defend areas by cones of machinegun fire close to the ground level. Leg injuries would be more common than all others combined under such circumstances.
Fragment-damage tables,8 published by the Office of the Chief of Ordnance, give the average distribution of effective fragments at various distances from the point of burst. With such tables, the distance at which a soldier has a given chance of being hit may be calculated. For example, a soldier is required to take a 1 to 100 chance of being hit by a fragment from a 20-pound fragmentation bomb. Suppose that the soldier is on open terrain in such a position that a 2-square-foot area of his body is exposed to fragments coming directly from the bomb. Under these circumstances, the effective fragments per square foot to which the soldier is exposed are 1/100 x ½ equals 0.005 per square foot. From the fragment-damage table for that bomb, it is found that the soldier should be about 150 feet from the bombburst. In the case of the 260-pound fragmentation bomb, he should be not less than 300 feet from the burst. Under similar conditions, the danger zone for a 75 mm. HE shell is approximately 100 feet and for the 105 mm. shell between 100 and 150 feet.
Depending on the orientation of the bomb or projectile at time of burst, effective fragment distribution varies considerably from the average on which the cited example is based. Effect of penetration before burst also is disregarded. In the most dangerous sector, fragment density may be increased as much as six times the average, increasing the danger zone severalfold. On the other hand, in the less dangerous zones, the fragment density is materially decreased.
In general, the wound factor varies something more than the square of the distance from the point of burst. Retardation of fragment velocity reduces the number of effective fragments, while the density per unit area of exposure also is affected by the distance from the point of origin. Fragment distribution too is materially influenced when a shell or bomb penetrates the ground appreciably before detonation.
The probability of a missile casualty as well as the character of a missile casualty also can be expected to vary from offensive to defensive warfare. The offensive soldier is of necessity more exposed. He is forced to advance in the face of prepared zones of fire, mined areas, and various protective devices calculated to minimize the exposure of the defenders.
In advancing, the experienced soldier takes advantage of all possible cover. However, he has to look for his enemy, so he must more or less expose his head. If ranges are sufficiently close to permit aimed shots, a preponderance of head casualties can be expected. This should be especially true of jungle warfare.
The Casualty Criterion
Terminal ballistics and the missile casualty become of importance to the military surgeon when the ordnance engineer asks for an opinion on the probable value of any given missile in producing a casualty. The ordnance engineer also requires a significant yardstick which may be mathematically applied in developing his designs of bullets, bombs, shells, grenades, or other missile casualty-producing agents.
Technical advancement has too often demonstrated the validity of the theoretical approach in design problems to permit the older rule-of-thumb or trial-and-error methods to be used in working up the instruments of modern warfare. Knowing the metal and detonating charge to be used in a given bomb, the ordnance engineer can readily calculate the number of fragments as well as their size and weight with probable distribution and velocities at any given distance from the point of burst. However, a criterion as to probable effectiveness is necessary if the data just cited are to be applied to practical design. During World War II, a criterion of a missile with weight and velocity sufficient to give it 58 ft.-lb. of kinetic energy was used in practice.
Though the adoption of the 58 ft.-lb. figure was arbitrary or empirical, it was much more practical than using the penetration of pine boards or other inanimate objects for the purpose. Selection of the figure was in a measure substantiated by the work of Gurney.9 This figure also was subsequently reasonably substantiated by the research of Harvey and his associates. It did supply a fully comparable yardstick on which to base theoretically relative efficiency.
A criterion of the potential wounding possibilities of a missile was first brought to the fore in the late 1920's when bullets of various calibers were under consideration in the development of a semiautomatic weapon. When this problem was presented to the U.S. Army Medical Department, it quickly became apparent that not only was there no criterion but that the military surgeon knew little, if anything, regarding the physical laws underlying the mechanics of wound formation or the production of a casualty.
For many years, ordnance engineers had been using the penetration of 1-inch pine boards separated by a small air space (1 inch) for judging the relative efficiency of bullets. Subsequent investigation revealed this test to be far from precise because of variations in pine boards, as well as many other factors beyond reasonable control. The motions of a spinning missile vary greatly as it passes through mediums of different densities or are modified by other variable physical characteristics. This greatly influences the retardation of the bullet and resultant conditions under which its kinetic energy is given up in the retarding material and influences the physical nature of the wound to a considerable degree.
Kinetic energy is computed from the formula mv2/2, in which m is the mass and v the velocity. It is noted that velocity plays much the greater part. If it is borne in mind that the usual bullet employed in military use varies in weight from around 135 to something more than 200 grains, the following tabulation showing the weight of missile necessary at various velocities to produce a kinetic energy of 58 ft.-lb. is of interest:
The fallacy of the pine-board penetration as a criterion of missile effectiveness was strikingly demonstrated quite accidentally when a shrapnel projectile was detonated in a close group of observers. The only real casualty was the man holding the projectile for he lost a couple of fingers from one hand. The shrapnel balls were well sprayed amongst the group of observers at close range and, yet, only a few black and blue places resulted-without penetration of the clothing. This total inefficiency of shrapnel was further demonstrated by study of known battlefield occurrences. However, shrapnel balls had penetrated many pine boards in the usual tests. Needless to say, the manufacture and use of shrapnel was promptly discontinued. In passing, it is also interesting to note that there is evidence of few true shrapnel wounds in World War I in which many tons of shrapnel were used. So-called shrapnel wounds on investigation were usually found to be due to HE missile fragments (table 19).
Distribution of Effective Missiles
In discussing the probability of a missile casualty, reference was made to fragment-damage tables. These tables are based on the assumption that a projectile or bomb breaks into a certain number of effective fragments and that the fragments are evenly distributed in all directions. In reality, this assumption is quite fallacious.
There is a marked variation in fragment distribution, even in the airburst. Sidewall fragmentation is quite different in character from that of base or nose fragmentation. Even in the light-case "blockbuster" bomb, there are differences in sidewall and nose or base fragmentation because of the relative thickness and distribution of the metal of the bomb. There also are fragments of
the fuze mechanism to be considered as these pieces are usually heavier and larger than wall fragments. They consequently have a greater danger range, and, while initial velocity may be slightly less, remaining velocity is better sustained because of greater mass.
Source: Terminal Ballistic Data, Office of Chief of Ordnance, Washington, D.C., 1945, vol. III.
Fragmentation bombs are specially designed to produce the greatest number of effective fragments in the sidewalls. Such bombs usually strike in a more or less nosedown position, so that nose fragments are necessarily forced into the ground. Tail fragments commonly fly up into the air and in falling are impelled only by the force of gravity so that their velocity is insufficient to produce more than minor casualties.
In the HE shells, both the base and the nose of the projectile are definitely thicker than the sidewalls. Sidewalls produce many more high-velocity fragments than either the base or nose. However, base and nose fragments, being larger, are less retarded in flight and have a correspondingly greater danger
range. Density of fragment distribution from the nose or base is less than in the case of sidewall fragments.
Rocket projectiles present another anomalous situation. Depending on the type of rocket, these projectiles have a velocity of 400 to 800 feet per second. They are fuzed with supersensitive fuzes so that they commonly detonate in the air, and the remaining velocity of the rocket affects the fragment velocities. This results in a distinct butterfly pattern of fragment distribution. The rocket sidewall section bursts into more than twice as many effective fragments as compared with the nose in the 4.5-inch HE rocket shell. At 20 feet from the burst, fragment velocities vary from 2,440 to 2,570 feet per second.
Fragment-damage patterns are published by the Office of the Chief of Ordnance. These show fragment distribution presupposing a graze or airburst close to the ground surface with a particular orientation of the projectile. Even under these ideal conditions, most damage patterns are of a distinct butterfly type. In some directions from the burst, there may be very few fragments, while in other directions there may be many effective fragments of a mass capable of maintaining a dangerous velocity over a considerable distance.
There is no allowance in the fragment-damage patterns for any earth penetration by the projectile or bomb before detonation. However, in almost every case, more or less penetration occurs, which materially modifies the damage pattern. In the case of large HE projectiles, there usually is so much penetration that almost all of the energy of detonation is expended in cratering the earth. Soldiers often expressed little fear for these larger shells as their antipersonnel effect was essentially nil, barring a direct hit.
With the usual contact fuze and even with the superquick contact type, there is sufficient delay in firing the bursting charge to permit considerable penetration, especially into soft earth. Standard-type fuzes operate progressively through primer and booster to fire the detonating charge. Some time interval is required to initiate a primer which in turn initiates the booster which fires the main charge. During the delay, the projectile or bomb can effect some penetration. For that matter, it also requires appreciable time for the main charge to rupture the holding case and set the fragments into motion. Slow-motion pictures readily demonstrate an appreciable timelag before fragments are flying freely accelerated to their maximum velocity. Case rupture takes place in a progressive manner requiring a lapse of time for its accomplishment.
Used only during the latter days of World War II, the proximity fuze appears to make possible the accurately controlled airburst of artillery projectiles and perhaps aerial bombs. This application insures an airburst with a much wider distribution of effective fragments. It can be expected that distribution will also follow a much more random pattern under these circumstances. This type of burst obviates the loss of effective fragments through "cratering" or the defilade effect of earth penetration.
PHYSICAL ASPECTS OF THE MISSILE
Motion of translation, velocity, is the only factor common to all missiles. It is probably the most important single factor in consideration of the missile as a potential casualty-producing agent. It is the major factor in making the missile capable of producing a wound.
For simplicity in discussion, velocities of less than 1,200 f.p.s. will be considered as low; those from 1,200 to 2,500 f.p.s., as medium; and velocities in excess of 2,500 f.p.s., as high.
Velocity is a continuously varying factor, and for ease in consideration as a function of the missile several phases of the missile trajectory will be discussed. First, the initial or muzzle velocity; second, the impact velocity or the speed of translation at the time the missile strikes a target; and third, the remaining (residual) or that velocity with which a missile leaves a target through which it has passed. In considering the missile and the production of a casualty, the second and third types of velocity are the more important. The impact velocity commonly determines the probable severity of a wound, while the difference between the impact and residual velocity determines the amount of energy doing work in producing the casualty. Initial velocity is important in that it insures an adequate impact velocity at the time a missile reaches the target. It also determines the probable danger range.
Initial velocity.-Initial velocity of a missile may be anything from a few feet a second up to much more than a mile a second. Small arms missiles have muzzle velocities ranging from around 800 up to approximately 3,000 f.p.s. Some of the recently developed AT weapons have muzzle velocities of slightly more than 5,000 f.p.s. Bomb fragments may have initial velocities of more than 7,000 f.p.s., and some of the fragments from HE artillery projectiles approach this initial velocity. Some artillery projectiles are launched with muzzle velocities greater than 3,000 f.p.s., though most have muzzle velocities between 2,500 and 3,000 f.p.s. The 21 cm. K12 German gun was credited with a muzzle velocity of 5,330 f.p.s. and a range in excess of 70 miles.10
In the antipersonnel weapon group, most sidearms, including the comparatively new carbines and small automatic weapons, launch bullets with muzzle velocities in the low-velocity category. On the other hand, most military rifles fire ammunition with muzzle velocities from 2,400 to 2,800 f.p.s. The older Japanese 6.5 mm. rifle fired ball ammunition with a muzzle velocity of 2,400 f.p.s., while most of the U.S. rifles and those of the Germans used ammunition with muzzle velocities near 2,700 feet per second.
Investigations in the late twenties and early thirties demonstrated the effectiveness of higher velocity missiles in the penetration of armor and led to
AT weapons of small caliber with velocities ranging from somewhat more than 3,000 up to more than 5,000 f.p.s. The soldier's inability to withstand more than a certain amount of recoil coupled with excessive barrel erosion accompanying the higher velocities operated to prevent the development of military weapons of the sidearm or shoulder type in this category for routine use.
High muzzle velocities in artillery weapons are seldom of more than didactic interest to the student of the missile casualty. Such velocities are usually for the purpose of increasing the effective artillery range, and at these excessive ranges the remaining projectile velocity is likely to be relatively low. Missiles from artillery projectiles attain their effective velocity more from the bursting charge in the projectile than from the motion imparted to the projectile in firing from the artillery piece. Suffice it to say that in general the higher the initial velocity of artillery ammunition, the more costly will be the gun that launches it. Such guns also have extremely short effective use periods without relining of the barrel, which is a major task.
Basically, most artillery has become primarily an antimateriel weapon with the antipersonnel characteristics only secondary factors. Of course, the exception to this is the target of massed men against which HE artillery projectiles are highly effective and their use militarily justified.
Initial or muzzle velocity is of interest only to the student of the missile casualty in that this velocity predetermines to a considerable degree the impact or effective velocity of the missile in producing the casualty. Once the accelerating force ceases to operate on a missile, deaccelerating forces take over, and the velocity is retarded. Retardation factors will be discussed later in more detail (p. 120). However, proximity to the missile source largely determines the impact velocity, and this in turn has much to do with the severity of the casualty. It is this proximity which makes the landmine a particularly vicious antipersonnel weapon. Velocities are high and missiles are many. The victim is often standing right over the mine or very close to it.
Impact velocity.-Of all factors to be considered in the missile casualty as a physical phenomenon, impact velocity is decidedly the most important. It determines the character of the wound and in turn only too often the fate of the victim. Research has demonstrated that a missile velocity of from 125 to possibly 170 f.p.s. is necessary to effect penetration of the human skin when using steel spheres one-sixteenth to one-fourth inch in diameter. Velocities of less than this produce only contusion without a break in the skin. Clothing also exerts a threshold penetration factor, at present undetermined. However, it is believed to be less than that of skin, which, comparatively speaking, is quite high. Of course, amount of clothing and its particular nature as well as other factors will affect the threshold velocity.
In the light of available information, few missiles with impact velocity of less than 200 f.p.s. are likely to cause more than a trivial wound in the clothed subject. Exceptions to this are the few missiles which may penetrate vital body cavities through apertures, or the more easily penetrated portions of the anatomy such as the eye.
The military surgeon is generally interested in missiles with impact velocities in excess of 200 or 250 f.p.s. In practice, it is probable that few wounds are caused by missiles with velocities much less than 500 f.p.s., and that most of the battlefield wounds are caused by missiles with velocities two and three times that figure. Some wounds are caused by missiles with impact velocities well above 2,500 f.p.s. High explosive shell fragments account for many wounds, and these velocities are apt to be well above 3,000 f.p.s. at near ranges. With the use of the proximity fuze in antipersonnel shells and aerial bombs, many missile casualties occur from fragments with velocities of 3,000 f.p.s. and upward.
With low-impact velocities, wounds are found to be relatively "cleaner" and free from the so-called explosive effect. With medium velocities, wounds are more extensive with considerable tissue destruction and with some explosive effects when conditions are favorable. High-impact velocities result in many so-called explosive wounds, with a maximum of tissue destruction.
Superhigh velocities make small missiles deadly. Comparatively, enormous tissue damage can result from the penetration of a very small fragment of a grain or so in weight when propelled at the supervelocities. In English bomb incidents, it was noted that minute missiles could be forced through the head with through-and-through wounds of the brain with slight, if any, visible evidence of a wound. The victims often walked away from the incident without even so much as a headache to show for the occurrence. It is known that the minute pins used by entomologists for the mounting of mosquitoes can be readily forced through a person's hand without evidence of blood or trauma and without sensation to the victim.
Remaining velocity.-Remaining velocity is of importance to the investigator in that it permits the determination of the kinetic energy expended in the production of the wound when a missile perforates a target. When a missile fails to pass through the target, all of the kinetic energy due to impact velocity is expended in wound formation. Apparently, the only fair measure of wound comparison on a physical basis is the expenditure of energy. Wounds cannot readily be compared on mere appearances alone, especially superficial appearances. In practice, remaining velocity can seldom be known, while in research it should always be measured or otherwise determined in some strictly comparable manner.
Momentum, Energy, Power
There has been much speculation and some observation as to the magnitude of the missile wound and its correlation with either the momentum, kinetic energy of the missile, or the rate with which energy does its work (power)-all physical attributes due to velocity. Momentum is a function of the mass times the velocity; energy a function of the mass times the square of the velocity; and the rate of doing work or power, a function of the mass times the cube of the velocity.
Before modern research, factual information on the various physical events actually occurring in the formation of a wound was lacking. Events transpire too quickly for the human senses to perceive the details. Earlier serious research studies had been inadequately instrumented to permit recognition of details. Results also were beclouded by the presence of indeterminate variables, such as deforming bullets, yaw, and other form factors.
To bring out and to evaluate fundamental postulates, basic research was conducted with nondeforming steel balls devoid of yaw or other complicated form factors. Simple mediums, such as water and 20 percent gelatin block tissue models, were used, as well as animal tissues. The cathode ray oscillograph and microsecond X-ray permitted the recording and accurate measurement of phenomena often completed in a few microseconds.
Results from this study were carefully analyzed, and it became apparent that all physical phenomena connected with the wound and its formation were direct functions of the kinetic energy doing work. Neither momentum nor the rate with which the energy did its work (power) could be correlated smoothly without excessive deviation with any of the various events which occur in the missile wound.
Hunters have entered into many acrimonious arguments on what constitutes an effective bullet in the taking of game. Here some claim that momentum is the factor. However, this opinion is believed to be due to the fact that hunters are continually observing the effects of bullets which usually deform seriously or more often break up on impact. In the latter case, the greater the mass, consequently the greater the momentum, the greater the apparent effectiveness of the bullet as it is less apt to disintegrate into such small pieces as to be almost useless after penetrating the hide of the animal. It is known experimentally that this last commonly occurs with the soft-nose hunting loads at impact velocities in excess of 2,000 feet per second.11
While velocity is the most important single factor in making the missile potent as a casualty producer, it attains that importance only through the fact that it gives the missile kinetic energy with which to produce the casualty. Physics recognizes two types of energy: Potential energy due to position and kinetic energy due to motion. The latter is computed from the formula mv2/2 (p. 112). In the English system, m is in pounds and v in feet per second. The corresponding results are in absolute units (poundals) which may be converted to the more conventional foot pounds by dividing by the acceleration due to gravity, (g) or 32.2.
From the formula, it is noted that kinetic energy varies as the square of the velocity. In practice, this means that doubling the velocity multiplies available kinetic energy by four. The following tabulation gives the kinetic
energy (ft.-lb.) at different velocities for a missile weighing 100 grains and readily demonstrates why small missiles become lethal at the higher velocities:
Kinetic energy varies directly as the mass of the missile. Hence, weight is of much less importance than velocity. Doubling the weight only doubles the energy.
Most bullets used by the military vary in weight from around 150 to approximately 200 grains. The corresponding kinetic energy at the usual initial velocities is between 1,500 and 2,500 ft.-lb., while some distance from the point of launching with lower impact velocities kinetic energies are much less, usually well under 2,000 ft.-lb. and often less than 1,000 foot pounds.
Again considering the tabulation just presented, it can be readily seen that considering the 150-200 ft.-lb. necessary for skin penetration that, at impact velocities of 7,000 f.p.s., missiles of less than 2 grains in weight are potential casualty-producing agents. This fact makes the modern bomb and artillery HE shells potent antipersonnel agents. At close ranges, there are many fragments which weigh at least 2 grains and which have velocities of 7,000 f.p.s. or more with the newer propellents. Multiple severe wounds can be expected.
With impact velocities of 5,000 f.p.s., missiles must weigh nearly twice as much to have energy equivalent to those at the higher impact (7,000) velocity. However, compared to the usual military bullet, these are still very small fragments.
The mass-velocity relationship and kinetic energy makes the landmine a particularly vicious weapon in that fragment velocities are of the order of 5,000 f.p.s., and there are many secondary missiles in addition to the fragments of the mine itself flying about with these supervelocities. Multiple severe wounds are to be expected, especially when the victim trips the mine by walking on it. In addition, there is quite an area within which missiles have velocities in excess of 3,000 f.p.s., and small objects can continue to be serious casualty producers.
Hand grenades with initial fragment velocities of 2,900 f.p.s. produce many fragments of a weight sufficient to have adequate kinetic energy to produce a severe wound. Grenades also are able to start effective secondary missiles into motion.
In HE shellburst with initial fragment velocities often a little more than 6,000 f.p.s., severe wounds are the rule. These too can readily produce severe casualties at the closer ranges.
Even water can be a casualty-producing missile when propelled with sufficient velocity. One of the more efficient metal-cutting tools is simply a small stream of water under high pressure (supervelocity).
Drag, Retardation, Ballistic Coefficient
Retardation varies directly as the square of the velocity and as the diameter of the missile. It varies directly as the density of the retarding medium and inversely as the mass of the missile. These are the more important factors affecting the retardation of a missile. They also largely determine the amount of kinetic energy which is utilized in the production of a missile casualty.
While complicated in detail, pertinent facts and relationships can be gained from a study of the formulas regarding the missile motions which are applicable to the military surgeon's study of the missile as a casualty-producing agent, as well as the wound as a physical entity. The following basic formulas are presented:
This formula applies particularly to motion in air and to
missiles without particular ballistic shape, such as spheres.
C = M / (kdrd2) or C = M / (id2) where i is a form factor. (3)
Retardation due to drag (D) then becomes
r = D / M = E(v) / C (4)
For the purpose of determining the factors controlling retardation, we will substitute the value of D in (2) for D in D/M in (4) which results inr = (kdrd2v2f (v/a)) / M (5)
In evaluating the effect of each of the several elements affecting retardation, the constants k and d may be disregarded. d2/M is simply another expression for the term "sectional density" (A/M where A is the area). Retardation decreases as this fraction approaches zero as a limit. Hence as d2 decreases, retardation decreases. In other words, the most efficient shape for sustained velocity is the needle or cylinder of maximum mass and minimum area of presentation.
Velocity of the moving projectile affects retardation as v2. The greater the velocity the greater the rate of retardation. Doubling the velocity multiplies the retardation factor by four.
During the air flight of a projectile, the density, r, is considered to be unity under average conditions near the ground. However, when considering retardation in a dense medium such as water or tissue, r is a factor of 800 or more.
Mach number, or the function v/a, is important in that it has been determined that the velocity of sound in a medium is a critical velocity. Using 1,100 f.p.s. as the average velocity of sound in air near the ground level, some values of v/a are tabulated:
From this tabulation, it is immediately apparent that a missile moving in air at 7,000 f.p.s. is retarded more than six times as quickly as the same missile moving at the rate of 1,000 f.p.s. This is an explanation of the fact that supervelocities and the consequent devastating wounds are only to be encountered quite close to the point of fragment departure. Supervelocity missiles are rapidly retarded to the lower velocities even in air.
Extrapolation of the formulas for the motion of a projectile in air to the motion in much denser mediums such as water and tissues is questionable. Too many little known, or unknown, factors are involved. However, by
collecting the unknown factors in KD, the drag coefficient (CD) in a dense medium may be represented by
where KD=summation of unknown factors affecting drag.
The drag coefficient can be determined experimentally when the velocity of a missile can be plotted against the time. Let a = the retardation coefficient and we have
dV / dt = aV2 (7)
For the determination of the drag coefficient we have:
a = (rA CD) / (2M)
High-speed motion pictures of missiles moving in water and gelatin gel have permitted the determination of dV/dt and from this a and in turn CD (6). The work was done with steel and aluminum spheres ranging in diameter from one-sixteenth to one-fourth of an inch. In water, CD was found to fall between 0.30 and 0.33 from a summary of coefficient data, and the observed value was 0.314.
While it is presumed logical that f(v/a) is equally applicable to retardation formulas pertaining to the denser mediums, its application is less important because of the usually higher value of a. In water, the velocity of sound is more than 4,500 f.p.s. and much greater than this in many metals and other hard materials. It is presumed that the velocity of sound in most tissues is similar to that in water, considering their average composition and density. In view of this, at most impact velocities, the factor v/a is less than one and comparatively unimportant in affecting retardation. For example, suppose v to equal 900 f.p.s. while a is 4,500 f.p.s. Then v/a equals 900/4,500 or 0.2.
This leaves as significant factors in considering retardation in dense mediums, r, and A/M and v2. Compared to air, r is much greater-800 or more. A/M and v2 retain their same significance.
In considering missile penetration of armor, concrete, and stone, other factors inherent in the material penetrated must be considered. Similar factors do not appear to be pertinent in tissue penetration with the possible exception of bone. However, for our purpose, any special properties of bone can be temporarily, at least, disregarded, as the extent of bone penetration compared to soft-tissue damage is usually insignificant.Shape
Random shape.-In shell or bomb fragments, pieces of glass, sand, and stones, missiles may have any possible shape. Few have the shapes or are so propelled that A/M or sectional density is a minimal value. Retardation in air is rapid. Table 20 illustrates how rapidly velocity falls with fragments from the burst of a 100-pound general-purpose bomb (the lightest effective fragment is one capable of penetrating ¼-inch mild steel).
Bullets, artillery projectiles, and rockets are launched point on so that the factor A/M is minimal. Bullets and artillery projectiles are further essentially stabilized in this minimal presentation through a high rate of spin about the long axis imparted by the rifling in the gun barrel. Random missiles seldom have a spin about the axis of flight but are more apt to whirl or tumble through the air. Retardation is more rapid because of the excessive area presented for the air to act upon.
Random fragments frequently have a shape conducive to excessive retardation as compared with the ideal form. Here the function v/a also plays an important role. The ideal shape when a is greater than v is the so-called teardrop section with the round portion to the front. When v exceeds a, the ideal shape is a pointed form, ogival or paraboloidal in section with the point to the front. For minimal retardation, surfaces should be smooth. Random missiles from bombs, artillery, and rocket projectiles are usually rough. Secondary missiles of sand and pebbles may be quite smooth and perhaps approach
the teardrop so far as leading edge presentation is concerned. Secondary missiles of glass may be quite pointed and are often likely to fly point on because of the vane action of their surfaces. In glass fragments, A/M may be favorable, A being minimal for the fragment and M fairly high considering the density of slightly more than 2 for glass as compared to nearly 8 for steel and more than 11 for lead. The density of sand is similar to that of glass.
Fragments consistently have less mass than bullets, size for size, owing to the approximately 50 percent greater density of lead as compared with that of steel, a representative fragment material.
Shell and rocket-projectile fragments are apt to be larger and consequently heavier than those from the usual general-purpose bomb and so have a better sustained velocity. Special antipersonnel aerial bombs may be constructed in such a fashion that fragments will be of a mass sufficient to sustain impact velocities at a level adequate to produce casualties at some distance from the point of burst. Also, through selection of metal and design, there can be some control of fragment shape. An instance of shape control is the corrugated casting used in the Mills hand grenade of World War I.
Ballistic shape.-The term "ballistic shape" as applied to missiles is employed to refer to those missiles specially designed to have the best possible exterior ballistic characteristics. In the missile-casualty field, the small arms bullet is probably the only missile falling properly in this category because of shape and controlled flight through spin imparted by rifling in the gun.
The effect of missile shape on retardation is strikingly shown in table 21 which lists the remaining velocities at different distances from the point of origin for fragments from a 4.5-inch HE shell and the Ml 150-grain bullet. Initial velocities are similar, approximately 2,800 f.p.s., in each case.
Three major types of shape are encountered in military small arms missiles: Flat base with-rounded nose; flat base with pointed nose; and tapered or so-called boattail base with pointed nose.
The first form is commonly used in sidearms, carbine, or other ammunition where velocities at battle ranges will be less than that of sound in air. The second shape was developed in the first decade of the 20th century to improve the flight of military bullets when muzzle velocities were developed to twice or more the velocity of sound in air. The taper-base bullet was a later development to permit of greater mass and better flight when the moving bullet was retarded to or below the velocity of sound in air. At first, many observers considered the taper-base bullet to be more accurate, but its accuracy was found to be due, in all probability, more to necessary improvements in manufacturing methods than to its shape alone. This bullet is slightly more stable in air flight because of the greater distance from center of gravity to center of pressure.
Careful analysis of bullets manufactured for match competition has demonstrated that care in base design and production is more important to accuracy than similar care regarding precision in the nose shape.
Theoretically, the bullet, or any projectile for that matter, to be accurate should be a perfect form of revolution with the center of gravity in the axis of revolution. While this attainment is approximated, perfection is impossible, especially in a missile assembled of various nonhomogeneous materials. Some asymmetry of mass distribution or shape or both is the rule rather than the exception.
Futhermore, when a bullet passes through the gun bore in launching, there is an asymmetrical engraving by the lands of the rifling. Again in manufacture, bullets are usually pressed into form at pressures of something less than 10 tons to the square inch. In firing, powder gas pressures against the base of the bullet are usually of more than 20 tons to the square inch. This results in deformation.
In the .30 caliber rifle barrel, the bore diameter is 0.300 inch and the groove diameter 0.308 inch. Bullets made of a homogenous material on a lathe and measuring 0.310 inch in diameter have been fired through accuracy barrels with a groove diameter of 0.308 inch and recovered after firing. On recovery, they still measured 0.310 inch in diameter, demonstrating either gun barrel stretch or temporary compression of the bullet or both.
Considerable heat is developed by the friction of the bullet in passing through the gun bore, and the temperature of the powder gases is high (above that of molten steel). There is some evidence that the lead core of bullets under certain conditions can be altered at least during the earlier portion of its flight. This permits some core deformation with consequent asymmetry of mass distribution.
Inherent and induced asymmetry in the bullet results in more or less yaw (deviation of the longitudinal axis from the line of flight) in the bullet during flight. Yaw is an important factor in the physical consideration of the bullet-produced wound and will be discussed later in greater detail (p. 127).
Table 22 shows the velocities of fragments of varying weight and random shapes at several distances from the point of a bombburst and demonstrates clearly the effect of mass (really the factor A/M) on impact velocities. The initial fragment velocity in all cases was 7,390 feet per second.
From this table, it is immediately apparent that at any given distance from the point of launching, initial velocities being comparable, the heavier missile will have the greater impact velocity. This follows from the retardation formula, retardation varying inversely as the mass.
Furthermore, the factor d2/M or A/M will consistently decrease as M increases, presupposing the fragment to be of the same material. Mass increases as the third power, while the corresponding area increases as the square. Doubling the size of a mass increases the weight eight times and the area four times in homologous shapes.
This principle underlay the development of the taper-base bullet. For instance, the .30 caliber flat-base bullet weighs 150 grains versus 172 grains for the taper-base bullet. Both have essentially the same bearing in the gun rifling, barrel friction is comparable, and gas check is equally efficient. In the German 7.92 mm. bullets, the weights are 154 grains for the flat-base versus 197 grains for the corresponding taper-base bullet. Impact velocities at any given range with these bullets will vary almost as the weight ratio, that is, as 172: 150 or 197: 154, if the bullets are launched with the same initial velocity.
Originally, the .30 caliber 172-grain taper-base bullet was loaded in ammunition for a muzzle velocity of 2,700 f.p.s., the same as that of the 150-grain flat-base bullet. For ballistic reasons, muzzle velocities were subsequently reduced to approximately 2,640 f.p.s. Some personnel also complained of recoil as being excessive and impairing marksmanship.
In this connection, it is to be noted that the recoil of a weapon is a function of the relative masses of the gun and bullet and the muzzle velocity of the projectile. Any decreases in weight of gun, increase in weight or muzzle velocity of the bullet will increase the recoil.
The Germans launched their 197-grain taper-base bullet with a muzzle velocity of approximately 200 f.p.s. less than that used with the flat base, 154-grain bullet (2,480 to 2,500 f.p.s.). The Japanese also launched their 196.9-grain 7.7 mm. taper-base bullet at a fairly low velocity, 2,239 feet per second.
Area of Presentation of Random Fragments
Theoretically, the area of presentation of a random fragment may be anything from a minimum (a) to a maximum (A) possible for any given fragment. However, mathematical investigation indicates that the average area of presentation in random fragments will be approximately 70 percent of A.12
Explanation for this lies in the fact that, because of the asymmetry of form as well as the unequal application of the impelling forces, fragments commonly have whirling or tumbling motions in addition to the motion of translation. In general, the greater the area of presentation in relation to the mass, the greater will be the retardation and the lower the impact velocity.
Shape can affect area of presentation. A round ball, for instance, has only one possible area. On the other hand, a rectangular object may have many possible areas of presentation from the minimum to the maximum section possible.
Bullets and projectiles are designed to afford the minimum area of presentation combined with the maximum possible mass. Minimum area of presentation is maintained through the action of the spin about its longitudinal axis imparted to a projectile by the rifling in the gun barrel. Rifling of a gun barrel was a major improvement accomplished in the latter part of the 18th century.
Yaw, deviation of the longitudinal axis from the line of flight, in a bullet without doubt plays a most important role in explaining many of the anomalies encountered in the study of bullet wounds. Yaw is increased proportionately to the relative densities of the retarding medium as compared to air, so in tissues it is augmented some 800 times, with resulting very complex, rapid bullet motions. This rapid, complex motion accounts for wound damage much more extensive than attributable to motion of translation alone. Yaw augments the retardation of a bullet in tissue, thereby materially increasing the amount of kinetic energy entering into the wound production.
Yaw results from two factors: (1) Spin imparted by rifling; (2) imperfections in the bullet due to construction or deformation in the bore of the gun and imperfections in the gun.
To have a yaw, a bullet must have a length greater than its diameter. There can be no yaw in a round ball. In flight, the forces of retardation can be resolved in a point within the moving object. In addition, there is within the solid the center of gravity and in the sphere the two points coincide, hence there is no lever between the two points about which an overturning force can operate.
In the bullet, or cylinder, in flight in a point-on orientation, the point at which the opposing forces are resolved will be different from the center of gravity. An overturning force will operate on the lever between these two points. Without spin, the bullet will tumble end over end.
With the muskets and smoothbore guns of the 17th and 18th centuries, round balls were employed. Bore diameters of guns were larger than in modern weapons, and powder pressures and velocities were comparatively low.
American hunters required accuracy and range. This naturally led to smaller bore weapons and longer barrels which, while decreasing the mass of the ball, resulted in increased velocities and range. As velocities are increased with the round ball in a smoothbore barrel, accuracy is lost. The ball may be quite erratic in flight. The idea of imparting spin to the missile by means of rifling naturally followed. This restored accuracy. It is now known that the inaccuracy of the ball is due to air piling up in front of it and that spinning the ball prevents this accumulation of air. The cylindrical bullet gradually evolved during the 19th century, and rifle calibers declined with powder improvement. The U.S. military weapon for some years was the Springfield .45-70, which fired a heavy lead bullet weighing more than 400 grains. This was followed near the end of the 19th century by the Krag-Jorgesen rifle of .30 caliber and a 220-grain jacketed bullet. In 1903, the Springfield magazine rifle of .30 caliber was adopted. At first, a rounded-nose bullet was used, but this was replaced in 1906 with the so-called spitzer bullet with an ogival head having the ogive struck with a radius of 7 diameters (calibers). This ogival head was developed in Germany early in the 20th century, and the first patent application in the United States was filed in 1905.
Most of this gradual change and improvement in bullets up to the period of World War I was largely accomplished by rule-of-thumb or crude scientific methods as judged by modern standards.
In the period of a little more than a century and a quarter following 1775, the following changes in military weapons slowly evolved:
1. The rifled bore, putting spin on the bullet.
During this transition, the pitch of the rifling was gradually changed until most military weapons used a twist of approximately one turn in a distance
of 30 calibers.13 While it is customary to state that the rifling makes a turn in so many inches, it is better to specify the pitch in calibers, which immediately permits of comparisons between weapons of differing calibers.
Pitch of rifling through determining the rate of spin is a factor in controlling the stability of the bullet in flight and in turn the degree of yaw on impact. The rate of spin in the usual military rifle is high. With the .30 caliber flat-base bullet at a muzzle velocity of 2,700 f.p.s. and a rifling pitch of 30 calibers, the spin is more than 3,500 revolutions a second. This spin is only adequate to stabilize the 150-grain bullet in air flight. The spin has a negligible effect in maintaining the bullet in a point-on position in denser mediums, such as water or tissues.
Spin maintains the bullet essentially in a point-on position through its effect on what is known as the overturning couple. In the elongated bullet, all retarding forces are resolved in a point somewhere in the axis of the bullet toward the nose. The center of gravity also will be in the axis but at a point nearer the base in the pointed-nose bullet. The distance between these points is the overturning couple, or lever arm, through which the forces resulting from the spin operate to stabilize the bullet.
Because a bullet is never a perfect form of revolution and because neither the center of pressure nor center of gravity is exactly in the axis, there is always some degree of yaw or tip or gyroscopic precession. Owing to the gyroscopic action of the high rate of spin, this yaw goes through a definite period which varies throughout the bullet's flight. Another factor inducing initial yaw is that, while the bullet passes through the gun barrel, the center of gravity is forced to travel in a circle so it will not be in the axis of the bore, whereas, once the bullet is in free air flight, the rotation is about the center of gravity, which immediately takes over.
Length of bullet determines the relative location of the centers of pressure and gravity and through that the length of the lever arm through which the forces of spin operate. This makes the longer, taper-base bullet somewhat more stable than the usual flat-base form.
However, density of resistant materials is a direct factor on the retardation and other motions of a missile. Water with a density 800 times that of air and tissues of slightly greater densities act much as a magnifying glass, magnifying all of the retardations, yaw, and gyrations of the bullet 800 or more times. A very slight tip or yaw will become one of more than 50° by the time a .30 caliber 110-grain solid bullet homologous in shape with 150-grain flat-base bullet has traversed 3 inches of water. Not infrequently, the increase in yaw will exceed 100°. Changing from one density to another also induces marked variations in the degree of yaw.
This, of course, immediately changes the area of presentation; a bullet enters tissue point on but in a few inches may be tipped up to 90° or more and the
presentation area is its broadside. The forces of spin are still operating, however, through the overturning couple and tend to stabilize and maintain the bullet in point-on flight. Consequently, in another few inches, the bullet is again point on and may leave the body through a small exit wound. Neither entrance nor exit wounds give any idea regarding the extensive interior destruction occasioned by the extreme tip and periodic bullet gyrations within the tissues.
While in flight, the bullet goes through all of the motions of the spinning top, except that it is much quicker because of its higher rate of spin. Some conception of the rate of spin may be visualized when it is realized that it is more than 100 times that of what is usually termed a high-speed electric motor armature which is rotating more than 1,700 revolutions per minute. The MII bullet with a muzzle velocity of 2,800 f.p.s. spins at a rate of more than 200,000 revolutions per minute. The usual top spins at a few hundred turns a minute but is relatively better balanced than the bullet.
When a top is started spinning, it wobbles more or less in a periodic manner. Then it stabilizes and, if well made, spins quite stably for an appreciable interval. Then, as it loses spin, it again becomes unstable and wobbles more and more as the spinning motion retards. The spinning bullet goes through similar gyrations while moving through the air. However, while the top goes through its gyrations with its point as a fulcrum, the fulcrum about which the bullet's axis tips is the center of gravity of the bullet.
These varied motions are gyroscopic in nature and strictly periodic. At one instant, the bullet is point on, and at the next instant the bullet axis is at an angle to the line of flight. This angle of yaw increases to a certain amount and then progressively decreases until it is again zero, when a node is reached and another similar gyration commences.
In air flight, degree of yaw is normally comparatively slight-less than 3° in properly designed military bullets. This spin is sufficient to stabilize the bullet in an essentially point-on position. The bullet goes through a complete gyration in a distance of 10 to 20 feet, at less than 0.001 second of time.
As the bullet leaves the muzzle of the gun, the actual angle of yaw is very small, only a few minutes of arc, but the angular velocity of yaw is considerable so that as the bullet moves along its trajectory the yaw increases until it reaches a maximum at some 10 or 15 feet in front of the muzzle. From here, it then proceeds to yaw in an approximately periodic manner throughout the remainder of its flight.
The angular velocity of the yaw is usually due to one of the following causes or a combination of them. It may be due to the fact that the axis of the bullet makes an angle with the bore so that the axis of the bullet is moving in a cone around the axis of the bore. This conical motion provides for the angular velocity just mentioned. Another cause is due to some asymmetry or inhomogeneity in the bullet which may result in the major axis of the ellipsoid of inertia of the bullet having a different direction from the axis of form. The result of this sort of angle is equivalent to the result produced when the axis of
the bullet makes an angle with the axis of the bore. The gyroscopic forces of spin quickly damp out the initial yaw so that at a distance of a hundred yards or so the bullet is flying almost exactly nose on.14
Bullet spin is retarded less rapidly than the motion of translation. However, at long ranges, several thousand yards or more, the bullet presentation is further complicated by the fact that the gyroscopic forces of spin tend to maintain the bullet's axis parallel to the axis of the gun throughout its flight. The axis of the bullet does not tend to follow the trajectory except for a short distance from the gun. As an example, if a bullet is fired from a gun elevated at an angle of 30°, the axis of the bullet tends to maintain this 30° angle throughout its flight. This results in asymmetry of the retarding air forces with respect to the bullet axis and consequent increase in angle of yaw at extreme ranges as the axis of the trajectory deviates from the direction of the axis of the gun bore.
Surgeons have often noted "key-hole" entrance wounds at extreme ranges and erroneously attributed them to "tumbling" bullets. In unimpeded air flight, a bullet given adequate initial spin seldom "tumbles" or flies end over end. Of course, a bullet often tumbles badly after striking a glancing blow in ricochet. However, at extreme ranges, a bullet seldom flies with its axis parallel to the ground, so often hits with its axis far from perpendicular to the surface struck. The entrance wound is usually an accurate record of the bullet's presentation at the instant of impact.
On entering a medium denser than air, all of these motions, especially the degree of yaw, are magnified. On entrance, yaw may be only a fraction of a degree, but it is quickly increased by approximately the ratio of the medium densities which for water and tissues is some 800 times. Likewise, period of gyration or distance from node to node is correspondingly shortened. A bullet may be essentially point on at impact and in a space of 3 inches be tipped in yaw at right angles to its line of flight and in another 3 inches again be essentially point on.
Moving from a medium of one density to that of another density influences the bullet's motions and can result in extreme angles of yaw. For instance, moving from air to tissue, from soft tissue to bone, and again from bone to soft tissue will have a profound influence in inducing extreme changes in the gyrations of the bullet and all of its motions, including retardation.
Retardation for any bullet also varies as the square of the angle of yaw in degrees so that a yaw of 13° will double the retardation.15 Letting δ be the angle of yaw in degrees, the retardation factor due to yaw is1 + (2) / (169)
Table 23 gives the retardation factor for varying values of yaw.
Yaws of more than 170° have been observed in bullets in passing through 6 inches of water. Theoretically, yaw can be of any value to just under 180 degrees. A yaw of 170° increases the retardation factors 172 times and a yaw of 179°, 190 times. This readily explains why a superspeed bullet is stopped in a very few feet of a homogeneous medium such as water.
This also explains why a supervelocity bullet is retarded so greatly in producing a casualty. The extreme retardation of such bullets can result in a wound with comparatively enormous destruction, tissue pulping, bone shattering, and other extreme manifestations only possible with the modern, fast-moving military bullet.
THE WOUND AS A PHYSICAL ENTITY
Permanent manifestation of the missile wound is a hemorrhagic area surrounding the track of cut and torn tissue left in the missile wake. However, while cutting through the tissue, a missile also imparts radial velocity to the tissue elements resulting in a development of a temporary cavity as the tissues absorb the kinetic energy lost by the missile through retardation. In absorbing this energy, some tissues more elastic than others react in such a manner that this cavity goes through several pulsations, each successive temporary cavity being smaller in volume than the preceding cavity. In longitudinal section, the temporary cavity is a conic section, usually an oblate ellipsoid in the case of a missile without yaw or particular form factor, such as a sphere.
In producing a casualty, the missile is commonly moving in the tissue a thousandth of a second or less, and the actual wound is produced too rapidly for human perception to appreciate all that goes on. As examples of actual time intervals involved, the following two instances are cited, considering the thigh with a thickness of 8 inches to be the part injured:
First, consider a bullet weighing 150 grains with an impact velocity of 2,500 f.p.s. and a residual exit velocity of 1,500 f.p.s. It will traverse the 8 inches of tissue and bone in 0.00033 second and expend 1,330 ft.-lb. of energy during its passage through the thigh.
Second, the same bullet with an impact velocity of 2,000 f.p.s. and an exit velocity of 1,000 f.p.s. will traverse the thigh in 0.00045 second, and 998 ft.-lb. of kinetic energy will be absorbed in the wound.
On dissection by the military surgeon, the most prominent feature of the wound will be the permanent cavity or wound track which on close inspection is found to be surrounded by a zone of more or less damaged tissues filled with extravasated blood. Partially or completely disrupted nerves may be found along with damaged blood vessels, though, barring a direct hit by the missile, most of the larger veins will be intact and the arteries uninjured. Bone may be found to be fractured without evidence of a direct hit. Such fractures are usually fairly simple, while those which result from a direct hit will show more comminution, especially at the cited impact velocities.
Research with spheres16 as missiles has demonstrated that both the volume of the permanent cavity and the tissue showing evidence of devitalization and extravasation of blood is a function of the kinetic energy entering into the wound; also, that the volume of the tissue showing extravasation is 11.8 times the volume of the permanent cavity. It is anticipated that with bullets the degree of yaw will modify the direct relationship between volume and impact energy or square of velocity.
Further research with steel spheres has demonstrated that, some 400 microseconds after impact, a temporary cavity some 26 times the volume of the permanent cavity reaches its greatest diameter perpendicular to the path of the missile. This cavity may go through several pulsations with corresponding negative and positive pressure phases. All of these phenomena are too rapid to be perceived by the human eye.
This temporary cavity and associated phenomena explain the so-called explosive effects often noted with high-velocity missiles. It accounts for tissue pulping and other damage some distance outside of the permanent cavity or apparent bullet track. During the stretching of tissue concurrent with the expansion of the temporary cavity, nerve trunks are often stretched to such a degree that function is destroyed without apparent gross injury.
As the missile tears through the tissues, there are two immediate results: (1) The cutting or tearing of a permanent cavity along its track; and (2) the initiation of severe shock waves, with pressures of well over 1,000 pounds to the square inch, which travel ahead of and out from the missile at the velocity of sound in the tissues, approximately 4,800 feet per second.
Experiment has demonstrated that for every foot pound of energy doing work in wound formation there will be a permanent cavity remaining with a volume of 2.547 x 10-3 cubic inches. With the average military rifle bullet and resultant wound, this presages a permanent cavity slightly larger in average diameter than the bullet. Yaw may modify the shape of the permanent cavity from point to point along the track, but the total volume should follow this expression as yaw also modifies the amount of energy doing work.
In the case of slow low-energy missiles, the permanent cavity will be distinctly smaller in diameter than the missile which produced it. Tissue elasticity accounts for the reduction in volume.
While the passage of the missile is responsible for the permanent cavity, it actually comes into permanent being sometime after the missile's passage. As the bullet passes through the tissue, considerable radial motion is imparted to the tissue elements, and a large temporary cavity is formed. Slow-motion pictures and other experimental evidence show that there are several pulsations before the wound track becomes wholly quiescent. This again is probably due to tissue elasticity, particularly the restraining action of the skin as it absorbs the energy imparted to it by the missile.
Area of Extravasation
On dissection of the wound track, the adjacent tissue is found to be quite sanguineous and, in the case of the average rifle-bullet wound, full of extravasated blood for an inch or more away from the track. In this region, histologic examination reveals a separation of muscle bundles with capillary hemorrhages into the interspaces.
In cross section of a wound track, this hemorrhagic area is found to be well defined. Experiment has shown that for every foot pound doing work in producing the wound there will be 30.105 x 10-3 cubic inches of this hemorrhagic tissue.
Survival studies have suggested that much of the tissue in this area of extravasation will regenerate if it is kept clean. However, in the battlefield, cleanliness is often impossible, and this pulped, hemorrhagic tissue provides an excellent pabulum for pyogenic bacteria and the clostridia which are responsible for gas gangrene. Early, adequate debridement is the indicated procedure in order to guard against secondary invaders and to insure early healing.
Microsecond X-ray and high-speed motion picture studies have demonstrated the formation of a temporary cavity with a volume almost 27 times larger than that of the permanent cavity. This cavity reaches its greatest size after the impact of the missile and after it has entirely left the wound track. Its maximum volume is 66.247 x 10-3 cubic inches for each foot pound doing work in producing the wound.
In the first hypothetical thigh wound (p. 133) in which 1,330 ft.-lb. of energy were expended, the temporary cavity would have a maximum diameter of perhaps 12 or 15 inches, depending on the presentation of the bullet. Its total volume would be 88.1 cubic inches.
This temporary cavity, long suspected but never before perceived in tissue, is the logical sequence to the passage of a missile through an elastic medium. Tissues are known to be quite elastic. The pulsation likewise is to be expected in some tissues, such as muscle, as would occur when a ball suspended by a rubber band is dropped. However, the pulsations damp out rapidly, and the human senses are only able to perceive that there has been some general disturbance of the tissues.
Shape of the temporary cavity is a function of the shape and presentation of the missile. With a sphere, the shape of the cavity is quite symmetrical-a conic section of revolution, fusiform in longitudinal section. In the case of a fragment, it may be quite asymmetrical as the presentation of the irregular fragment varies. In the case of the bullet, yaw will result in asymmetry. In fact, where the bullet goes through a node and then again into yaw, there may be several larger temporary fusiform cavities connected by much smaller ones, the so-called scalloped wound remaining in the permanent cavity. Variations in tissue also affect the type and shape of cavity.
This cavity is the result of particles set into motion by the passage of the bullet. Time is required to overcome their inertia, hence the lag in full development of the temporary cavity as compared to the passage of the bullet. While the missile imparts outward moving forces to the particles at the instant of its passage, it requires some microseconds for the particles to move outward to their greatest distance and for the physical properties of the tissues to absorb the forces involved. Average particle velocities are not particularly great. In the hypothetical thigh shot, they would be 125 feet per second.
While foot pounds, units of energy, have been used in discussing the mechanics of the missile wound, a better conception of the magnitude of the forces involved may come from a consideration of the power utilized in wound formation. Power is the measure of work done by the energy expended by the missile in the wound. The 1,330 ft.-lb. absorbed in 0.00033 second in the first hypothetical wound is the equivalent of some 7,200 horsepower of work. In the second wound (p. 133) with 998 ft.-lb. absorbed in 0.00045 second, the work equivalent is more than 4,100 horsepower. Work done in any missile wound will seldom be less than several hundred horsepower and will often considerably exceed the figures cited. The larger numerical values of horsepower can be expected when it is realized that 1 horsepower is the lifting of 550 pounds for 1 foot in 1 second. In the wound, more than 1,000 ft.-lb. of energy may do its work in much less than one-half of a thousandth of a second.
With this realization of the forces involved in the production of the missile casualty, some of the otherwise anomalous manifestations in the wound appear much more logical. For instance, fractures occur at some distance from the
missile track and without any direct contact between the bone and the missile. Forces may be transmitted through the essentially noncompressible blood and rupture a vein some distance from the missile's path. Nerves may be paralyzed and yet fail to show gross evidence of physical damage. In some wounds in muscle, splitting along fascial planes will be noted for a considerable distance from the path of the bullet.
Fluid-filled viscera are often blown asunder by the operation of hydraulic forces. High-velocity missiles may pulp the brain substance. In some cases, the bones of the skull are separated along the suture lines as though an explosion has occurred within the brain case. This is but another manifestation of the forces operating in the formation of the temporary cavity, and examination often reveals clean holes of entrance and exit of the missile showing that the bony rupture occurred after its passage. Similarly, in shooting through a can filled with water, the rupture of the can occurs after the through-and-through passage of the bullet.
Knowing the relationship between the permanent cavity, zone of extravasation, and temporary cavity, the military surgeon can make use of this knowledge in determining the extent of the wound. The zone of extravasation is readily seen and can indicate the total involvement. For instance, if an area of tissue full of extravasated blood is seen extending for a distance of 2 inches from the axis of the permanent cavity, it is known that damage along fascial planes, perhaps some blood vessel rupture, and some nerve injury can be expected to a further distance of some 2½ inches beyond the zone of extravasation. If note is made of the extent of extravasation, some idea as to the amount of energy expended in the wound is determinate.
The military surgeon should never be misled, especially in the case of bullets, by small entrance and exit wounds. These small skin openings may be no indication whatever of the possible extent of the internal wound. This is particularly true of the yawing bullet and may be true of the high-velocity, spinning fragment. Elasticity of the skin often results in almost complete closure of skin wounds.
Temporary Cavity Pulsations
In water and certain tissues, such as the muscular thigh surrounded by highly elastic skin, the temporary cavity goes through a series of pulsations. As the cavity expands, a negative, subatmospheric gage pressure develops within the tissues. This is followed by a positive pressure of greater intensity but of shorter duration with the collapse of the cavity. In water, these pulsations may continue for as many as seven or eight cycles, disappearing as the cavity disintegrates. While measurements of tissue phenomena have not been made as complete as those in water, definite indications are that the tissue often behaves in a manner wholly analogous to water. There may be two or more pulsations.
For water, the period of the pulsations is related to the amount of energy doing work. The time of a cycle in seconds is equal to 2.35 x 10-3 times the cube root of the foot pounds of energy absorbed. This relationship also is reasonably applicable to most tissue wounds. The following tabulation gives the computed time of a complete pulsation in milliseconds for varying amounts of energy in foot pounds:
Coupled with the temporary cavity in water and its pulsations there are internal pressure changes. When the cavity is fully expanded, pressures in the medium are at their lowest value, often a full atmosphere or more subnormal. As the temporary cavity decreases in size, pressures increase reaching a maximum value of three or four times atmospheric pressure. Oscillograms reveal that, while the positive pressures are greater in intensity, the duration of the negative pressure phase is twice as long.
While the initial shock wave shows very high pressures (1,000 pounds per square inch and more), oscillograms show its duration to be short, 15 to 25 microseconds. Available evidence indicates that this short duration may explain the apparent fact that little if any true tissue damage in gas-free tissues can be attributed to this initial shock wave despite its intensity. Other studies have shown that tissue elements withstand much higher static pressures without damage.17 However, when gas is present in the tissue, damage often occurs.
Experimental studies afford quite conclusive evidence that subatmospheric pressures connected with cavity behavior are responsible for much tissue destruction.
Though cavity pulsation has been detected in water, in gelatin block and in some tissues, in abdominal shots in the cat, no pulsations were noted in microsecond X-rays. Here, a single temporary cavity followed by rapid collapse appears to be the rule. However, extensive damage to the intestines occurred which was due largely to the expansion of gas in the intestines in the subatmospheric pressures during the expansion of the temporary cavity and following the shock wave. This expansion of gas results in great stretching of tissues and consequent rupture or other severe damage. This stretching is not due directly to either the shock wave or cavity formation behind the missile but rather to the expansion of the air pocket already present within the tissues. This air responds to the pressure changes around the temporary cavity, and the stretching occurs as the result of the subatmospheric pressures when the included air expands.
Though not established experimentally, it is anticipated that the subatmospheric pressures may likewise lead to sudden expansion of gas in the alveoli in the lungs so as to stretch the walls and rupture small blood vessels. Such injury is indicated from field observations.
The extent of the temporary cavity formation and the relationship of tissue damage to the permanent wound track may be influenced by constricting clothing, tenseness of muscles, or other variables at the time of wounding. For instance, removing the skin from a cat's leg before wounding resulted in a larger temporary cavity with more of a wound "blow-out." On the other hand, reinforcing the skin with Scotch tape changed the shape of the cavity and resulted in tissue damage to a greater distance from the missile track. Elasticity of the skin and muscle fibers appeared to play a considerable part in predetermining the physical nature of the missile wound.
Skin Penetration and Energy Absorption18
Skin and bone both appeared from experimental data to offer a particular resistance to penetration differing from other tissues. There was a critical velocity in each case below which a missile would not effect penetration. There was comparatively little difference in the value of this critical velocity irrespective of the size of the missile.
Initial velocity required for a 4/32-inch steel sphere weighing 2 grains was found to be 170 f.p.s. for penetration of human skin. Lead spheres having an 11/64-inch diameter, weighing approximately 7 grains with a velocity of 161 f.p.s., did not effect penetration. Even extremely large missiles will lose about 125 f.p.s. of their impact velocity in penetrating the surface of the skin. Area of presentation affects skin penetration to such degree that the loss in velocity is proportional to the reciprocal of the diameter of the spheres.
Skin was found to be more resistant than other tissues. The drag coefficient, a value dependent on the resistance encountered by a missile and independent of the missile, for human skin was 0.528 as compared to 0.297 for water. The coefficient for cat muscle was 0.448 and for 20 percent gelatin block, 0.350. Human skin had a drag coefficient more than 20 percent greater than cat muscle. While the drag coefficient was not determined, indications were that cat skin was slightly more resistant to penetration than human skin.
The skin resistance offered a logical explanation for the fact that shrapnel, formerly used as an antipersonnel agent, was commonly ineffective. It was usually employed at such ranges that remaining projectile velocity was low. The bursting charge propelling the shrapnel balls was commonly incapable of imparting sufficient velocity to effect skin penetration. Shrapnel balls also had a poor ballistic shape and were rapidly retarded in air flight.
An anomaly in skin penetration was the threshold velocity necessary to effect penetration, rather than a certain amount of energy. A 2-grain sphere required a velocity of 170 f.p.s. for penetration or a negligible amount of energy when measured in foot pounds. For a 150-grain bullet to penetrate skin, a velocity of approximately 125-150 f.p.s. was required corresponding to approximately 5 ft.-lb. of energy. The 2-grain sphere would have less than one-fiftieth this amount of energy.
Bone offered a situation similar to that found in skin. Here a minimal velocity of approximately 200 f.p.s. was necessary to effect penetration. Once penetration had been effected, any velocity remaining above the 200 f.p.s. would operate to effect deeper penetration in direct proportion to the square of the velocity and the sectional density of the missile. Penetration and damage to bone was effectively gaged by the amount of energy performing work, essentially proportional to the square of the velocity.
While specific experiments were conducted with beef bone, results are substantiated by other work with human and horse cadavers. Results were essentially the same.
In conjunction with these critical velocities necessary to effect penetration, some consideration should be given to the .45 caliber automatic pistol and its load. From time to time, complaint has been registered that this weapon is not as efficient under all conditions as could be desired in a self-defense weapon. A 234-grain full metal patch bullet is used, and it is launched with a muzzle velocity of 825 feet per second. Following is a tabulation of the kinetic energy available with this bullet at various velocities:
Considering the 125 f.p.s. required to effect skin penetration, it can be seen that the remaining velocity and energy are dropped down to at least 700 f.p.s. and 254 ft.-lb., respectively. The penetration of bone requires another 200 f.p.s. and dropping remaining velocity to 500 f.p.s. and energy to 130 ft.-lb. In addition to these losses, passage through tissue results in some retardation, so remaining velocity and energy will certainly be something less than the figures cited. Furthermore, impact seldom occurs at pointblank ranges, and
the initial velocity is certain to be something less than 825 f.p.s. when the bullet hits the skin.
From an analysis of these facts and the requirements for penetration of skin and bone, it can be readily appreciated that the .45 caliber bullet is of little value as a wound-producing agent except in the softer tissues and at near ranges. The bullet often fails either to penetrate or to fracture bone and practically never shatters bone in the manner common to the rifle bullet or fragment. The Japanese and German sidearms with muzzle velocities of approximately 1,100 f.p.s. were much more effective as antipersonnel weapons than the .45 caliber weapon. While the same bullet with its characteristics was used in the submachinegun, multiple hits probably compensated for the weaknesses, so apparent in single shots.
Of course, the carbine with its much higher muzzle velocity has largely replaced the .45 automatic pistol and is a more effective antipersonnel weapon than any of the sidearms.
Histologic Character of Tissue Damage
Muscle damage is evidenced by swelling and coagulation in a region a few millimeters from the permanent cavity of the wound. Often, no muscle damage is noted in regions where blood extravasation from ruptured capillaries is pronounced.
Expansion of the temporary cavity along fascial planes results in an accumulation of blood from the rupture of small blood vessels, but the larger vessels are remarkably resistant to injury, probably because of their elasticity. Sometimes, a blood vessel is left spanning a permanent cavity. In other cases, nerves are severed, while blood vessels running parallel with the nerve in the same fascia are intact. Veins with their comparatively thin walls often rupture as the result of transmitted forces, while arteries with their more resistant walls are usually patent barring a direct hit.
Cavity Formation by the Moving Missile
As a function of the amount of kinetic energy doing work, the speeding missile results in a permanent cavity, a zone of tissue full of extravasated blood, and a temporary cavity in tissue. In water, it also produces a cavity. The volumes of the various cavities in cubic inches are related to the foot pounds of energy expended by the following formulas:
Table 24 shows the comparative volumes of the various cavities in cubic inches for varying amounts of energy expended.