Emergency War Surgery NATO Handbook: Part I: Types of Wounds and Injuries: Chapter II: Missile-Caused Wounds

Projectiles

United States Department of Defense

The following is a compendium of the characteristics of the more commonly encountered small arms projectiles. Note that the projectiles depicted in Figures 4 - 9 do not deform upon passing through soft tissues, whereas those in Figures 10 - 14 either deform or fragment, forming secondary bullet fragments. Projectile deformation, fragmentation, yaw and individually or collectively increase the resultant degree of tissue disruption.

45 Automatic - This full-metal-jacketed military bullet (Figure 4) is one of few that does not yaw (turn the long axis in relation to direction of travel) significantly in soft tissue. Lack of yaw, coupled with the large mass of this bullet, results in deep penetration. The crush tissue disruption remains nearly constant throughout the bullet path. Temporary cavity stretch is maximal near the point of entry, gradually diminishing with penetration, but with this bullet type and velocity the temporary cavity is too small to show a stretch wounding effect.

Figure 4

22 Long Rifle - This commonly used rimfire bullet (Figure 5) yaws through 90 degrees and ends up traveling base forward for the last half of its tissue path. The crush tissue disruption increases with yaw angle, reaching its maximum when the bullet is traveling sideways. Temporary cavity stretch increases with increasing bullet yaw, much the same as a diver hitting the water makes a larger splash as his body angle to the water surface increases. Even at the point of maximum bullet yaw, the temporary cavity produced remains too small to add a detactable stretch wounding effect.

Figure 5

38 Special - This round-nosed lead bullet (Figure 6), like the 45 Automatic (Figure 4) and the 22 Long Rifle (Figure 5), produces its wounding almost solely by the crush tissue disruption mechanism. Although still too small to show an observable stretch wounding effect, the maximum temporary cavity is of 20% greater diameter than that made by the 22 Long Rifle despite the fact that its velocity is 40% less.

Figure 6

9 mm Parbellum - This bullet is widely used in both pistols and submachine guns. As with the full-metal-jacketed bullet type, it produces a profile that resembles that of the .38 Special (Figure 6), but the maximum temporary cavity is about 2 cm larger in diameter and will show some stretch effects (radial splits) in less elastic, more susceptible tissues such as those of the liver.

7.62 NATO FMC - FMC is the abbreviation for full-metal-cased, which is a synonym of full-metal-jacketed. This refers to the harder metal covering of the bullet core. This full-metal-jacketed military bullet (Figure 7) shows the characteristic behavior in tissue observed in non-deforming pointed bullets. It yaws through 90° and, after reaching the base-forward position, continues the rest of its path with little or no yaw. The bullet is stable traveling base first in tissue, since this position puts its center of mass forward. The rotation imparted to the bullet by the rifled gun barrel is sufficient to cause point-forward travel in air, but not in tissue where such factors as bullet shape and location of center of mass outweigh rotation effects. The tissue disruption in the first 15-18 cm of bullet penetration, during which the streamlined bullet is still traveling point forward, is minimal. At 20-35 cm, however, in which bullet yaw is marked, a large temporary cavity is produced. If the bullet path is such that this temporary cavity occurs in the liver, this amount of tissue disruption is likely to make survival improbable.

Figure 7

AK-47 - The Russian Assault Rifle's full-metal-cased military bullet (Figure 8) travels point forward for 25-27 cm in tissue prior to beginning significant yaw. Wounds from this rifle are familiar to surgeons who served in Vietnam and have been documented by the WDMET study of wounds from that conflict.

Figure 8

AK-74 - This new generation, smaller caliber Russian Assault Rifle (Figure 9) follows the example set by the USA with the M-16. The full-metal-cased bullet designed for this weapon has a copper-plated steel jacket, as does the bullet of its predecessor, the AK-47. A unique design feature of the AK-74, however, is an air space (about 5 mm long) inside the jacket at the bullet's tip. The speculation that this air-space would cause bullet deformation and fragmentation on impact proved to be unfounded, but the airspace does serve to shift the bullet's center of mass toward the rear. This bullet yaws after only about 7 cm of tissue penetration, assuring an increased temporary cavity stretch disruption, even in many extremity hits. The typical exit wound from a soft-tissue thigh wound (12 cm thick) is stellate, with skin split measuring from 9-13 cm across. The underlying muscle split is about half that size. The bilobed yaw patterns shown in the profiles of the AK-47 and the AK-74 represent what is seen in four-fifths of test shots. In the rest, the bullet reaches 90° of yaw and continues to 180° or the base, forward position, in one cycle. Whether there are one or two yaw cycles does not influence the point of prime clinical relevance- the distance the bullet travels point forward before yaw. The bilobed yaw pattern depicted in Figures 8 and 9 results from initial bullet yaw returning to zero yaw (first lobe), but then yawing a second time (second lobe) to 180° where the center of mass stabilizes the projectile in base forward navel.

Figure 9

357 Magnum JSP - The jacketed soft-point bullet (Figure 10) and the jacketed-hollow-point bullet flatten their tips on impact. This "expansion" or "mushrooming" (in which the final bullet shape resembles a mushroom) results in a doubling of effective bullet diameter in tissue, and allows the bullet to crush four times as much tissue (¹ times radius squared equals the cross section area of the bullet which impacts tissue). This conversion of the bullet to a non-aerodynamic shape causes the same sort of increased temporary cavity tissue stretch as does the yawing of a bullet. The maximum temporary cavity produced by the expanding bullet occurs at a shallower penetration depth than that caused by the full-metal-jacketed military type bullet. This soft-point pistol bullet is typical of the type most commonly used by law enforcement agencies in the USA. Its decreased penetration depth, as compared to the depth of penetration of the nondeforming bullets depicted in Figures 2 and 4, decreases the likelihood of the bullet perforating a criminal and going on to injure an innocent bystander.

Figure 10

7.62 SP - (SP is the abbreviation for soft-point) The same cartridge case shown in Figure 7, when loaded with a soft-point bullet, produces the wound profile shown in Figure 11. Changing only the variable of bullet construction causes massively increased tissue disruption compared to that of the full-metal-cased bullet (Figure 7). Bullet expansion occurs on impact as seen with the 357 Magnum pistol bullet (Figure 10); however, the crush in the tissue that results from bullet expansion accounts for only a small part of the large permanent cavity. As this bullet flattens, pieces break off and make their own separate paths of crushed tissue. These bullet fragments penetrate up to 9 cm radially from the bullet path. The following temporary cavitation stretches muscle that has been weakened by multiple perforations. The fragment paths act to concentrate the force of the stretch, increasing its effect and causing pieces of muscle to be detached. This synergistic effect, resulting in the large tissue defect shown in Figure 11, is seen only with bullets that fragment. The 7.62 NATO soft-point is a popular big game hunting bullet, and although shooting accidents are not infrequent with such rounds, they are rarely seen in the hospital since few victims of torso shots survive.

Figure 11

22 CAL FMC - This is the M-193 bullet shot from the M-16A1 Assault Rifle (Figure 12). The large permanent cavity shown in the profile was observed by many surgeons who served in Vietnam, but the tissue disruption mechanism responsible was not clear until the importance of bullet fragmentation as a cause of tissue disruption was worked out. This military round is full-metal-jacketed and, as with other bullets of this type, it causes little tissue disruption so long as it remains traveling point forward through tissue. Its average distance of point-forward travel is about 12 cm, after which it yaws to 90°, flattens, and breaks at the cannelure (groove around bullet mid section). The bullet point remains a flattened triangular piece, retaining about 60% of the original bullet weight. The rear portion breaks into many fragments that penetrate up to 7 cm radially from the bullet path. The temporary cavity stretch, its effect increased by perforation and weakening of the muscle by fragments, then causes a much enlarged permanent cavity by detaching muscle pieces. The degree of bullet fragmentation decreases with increasing shooting distance, as striking velocity decreases. At a distance of 80 meters, the bullet breaks in half, forming two large fragments. At ranges in excess of 180 meters, this projectile does not break in two and the wounding capacity and mechanisms are essentially the same as those of the AK-74.

Figure 12

M-855 22 CAL FMC - The slightly heavier M-855 bullet shot from the M-16A2 Assault Rifle will eventually replace the M-193 bullet shot as the standard bullet for the U.S. Armed Forces. The wound profile is similar to that produced by the M-193, although the tip generally does not remain in one piece. The temporary cavity size and location are about the same and any difference in wounds caused by the two would be cliff cult to recognize.

The smaller bullets of the new generation Assault Rifles (M-193, AK-74, M-855) are susceptible to deflection and disturbance of their point-forward flight by intermediate targets such as foliage. This was not the case with the previous generation of larger and slower projectiles. This can result in large yaw angles at impact and a shallower location in the body of maximum tissue disruption. For these bullets that rely on yaw in tissue for their maximum effect, the wound profiles show the average penetration depth at which this yaw occurs.

.224 Soft-point - This 50 grain soft-point bullet is designed for maximum deformation and fragmentation. To produce the wound profile shown in Figure 13, it was shot from the M-16 cartridge case (known as the 223 Remington in civilian shooting parlance). The amount and type of damage caused is about the same as that caused by the military M-193 (M-16) bullet, but the location of the maximum disruption is at a shallower penetration depth.

Figure 13

12 Gauge Shotgun #4 Buckshot - Loaded with 27 pellets of #4 Buckshot (Figure 14), the 12 gauge shotgun at close range (3 meters in this case) causes massive crush type tissue disruption. At this short range, soft- tissue impact deforms the individual pellets, increasing their original 6 mm cross section to about 10 mm with concomitant increase in tissue crush or hole size. The 27 perforations of this size in a 7-8 cm diameter area result in severe disruption of anatomy by direct crush and in disruption of blood supply to tissue between the multiple wound channels.

Figure 14

The foregoing wound profiles portray an estimate of the maximum soft-tissue disruption expected at short ranges (under 25 meters). A gradual decrease in the amount of bullet deformation, fragmentation, and maximum size of the temporary cavity occurs with distance as the striking velocity of the projectile decreases. When bone is struck by the penetrating projectile, the result is predictable and easily verified on X-ray. Total penetration depth will be less; however the degree of tissue disruption will be greater due to increased ,projectile deformation and the creation of secondary bone fragment missiles.

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Operational Medicine 2001

Health Care in Military Settings

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