Sobchak Security

Military Medicine, Aug 2007
by Dougherty, Paul J, Matthews, Bradford K

Objective: Concerns about altered wounding characteristics of the M-4 carbine have been raised during recent deployments. Using the wound profile method, the purpose of this study was to compare the M-16A2 rifle with the M-4 carbine. Methods: The M-4 carbine and M-16A2 rifle were compared by firing five shots each into calibrated 10% ordnance gelatin at a distance of 3 m. Measured parameters included temporary cavity, projectile velocity, penetration depth, and bullet fragmentation. Results: The M-16A2 rifle produced a higher muzzle velocity (3,155 ft/s vs. 2,848 ft/s; p

Introduction

Scientific wound ballistics studies have been conducted by medical personnel since the late 19th century in an effort to understand mechanisms of injury from gunshot wounds.1 Medical personnel are concerned about the pathophysiology of any disease process, whether this is breast cancer or a gunshot wound, to better care for patients. Understanding the projectiletissue interaction and the factors involved in the production of a wound is important for those who treat gunshot wounds. Knowledge of wounds produced on the battlefield by specific weapons allows physicians to better predict a patient’s clinical course.2-9 Other areas of wound ballistic studies include the epidemiology, clinical course, and outcome of patients who sustain ballistic injuries.5,7,9

The wound profile method was developed at Letterman Army Institute of Research during the 1980s, in an effort to illustrate the wounding patterns of various firearms.2″6 This method, using 10% (by weight) ordinance gelatin at 4�C, accurately simulates soft tissue injury. It is a useful method for educating medical personnel about a weapon’s effect and demonstrates the types of wounds that may be seen. Additionally, this technique has been used to help with forensic cases.2-6,10

In 1994, the U.S. military adopted the M-4 carbine (Fig. 1), a shortened version of the M-16A2 rifle (Fig. 2), to provide a more compact arm for vehicle crewmen and those not requiring a full-size weapon. The M-4 carbine has also been used by U.S. Special Operations Command and counterterrorist and Special Forces units, which also seek a compact weapon. The M-4 carbine has a shorter barrel than the M-16A2 (370 mm vs. 508 mm), as well as a collapsible stock.

The first combat use of the M-4 in Afghanistan in 2001 and 2002 raised serious concerns about the wounding effects or “stopping power” of the new arm, in comparison to the M-16A2 rifle, in both the official and lay press.11-13 For example, the April 2002 presentation at the Natick Solider Center by LTC Charlie Dean and SFC Sam Newland reported on lessons learned regarding M-4 carbine use in Afghanistan during Operation Anaconda. Although 89% reported satisfactory confidence in their weapon, 20% were dissatisfied with the use and ultimate effectiveness regarding “lethality” and “incapacitation.” From a medical standpoint, the wounding potential of the M-4 carbine had not been compared with that of the M-16A2 rifle.13

To our knowledge, a comparison of the wounding potential of the two arms had not been conducted before the first use of the two weapons by U.S. troops in Afghanistan. The objective of this study was to compare the wounding potential of the M-4 carbine and the M-16A2 rifle using the wound profile method.

Methods

The wounding characteristics of the M-4 carbine and M-16A2 rifle were compared by using the wound profile method. This technique is a validated accepted method that can accurately represent wounds in soft tissue.2-4,10 It was developed at the U.S. Army Medical Department Wound Ballistics Laboratory (Letterman Army Institute of Research) in the 1980s and has become the accepted standard wound simulant for both medical and law enforcement communities.

Using this method, shots were made into blocks of ordnance gelatin prepared to reproduce the wounding characteristics of soft tissue. Ordnance gelatin was prepared by adding 25OA ordnance gelatin powder (Kind and Knox, Sioux City, Iowa) to water in a 10% (by weight) mixture. The ordnance gelatin blocks were formed in a mold, giving the shape of 50 cm � 25 cm � 25 cm. The blocks were kept in a refrigerator at 4�C, allowed to cure, and then removed from the molds and placed in plastic bags to avoid dehydration. The blocks were returned to storage at 4�C. The blocks were then transported to the range in an ice chest to prevent warming and were used within 20 minutes after removal from the chest.2-4.10 The current 5.56-mm M-855 cartridge (Lake City, Independence, Missouri) was used for all shots in this study. To minimize variation, all cartridges were from the same lot of ammunition. All shots were made at a distance of 3 m from the muzzle to the face of the ordnance gelatin blocks.

Calibration of the ordnance gelatin was performed by shooting BB shot into the gel before testing and measuring the penetration in comparison to velocity. All blocks were calibrated to ensure that there was minimal variation between blocks. After calibration, the gelatin blocks were ready for terminal ballistics testing.

Measured parameters included the temporary cavity, neck length, projectile velocity, penetration depth, and bullet fragmentation (Fig. 3). The temporary cavity was quantified by measuring the radial splits (in centimeters) in the gelatin after dissection. The radial splits in 10% ordnance gelatin have been correlated with skeletal muscle wounds in a limb. The temporary cavity represents transient lateral displacement of tissue that occurs after passage of a projectile. Elastic tissue, such as skeletal muscle, skin, nerve, and blood vessels, rebounds from the displaced position after passage of the projectile. Inelastic tissue, such as bone and liver, fragments in this area. Neck length is the length (in centimeters) of tissue or simulant that a bullet traverses before it begins to tumble. Projectile velocity was measured by using an Oehler 33 series chronograph (Oehler and Co., Austin, Texas). Penetration distance was measured (in centimeters) from the face of the gelatin block. Fragmentation was quantified by photographing the blocks and weighing the major recoverable fragments, to the nearest grain, on an electronic scale. Statistical comparisons of data between the two firearms were made by using Student’s t test.

Results

Five shots from both the M-4 carbine and the M-16A2 rifle were made into the calibrated ordnance gelatin blocks. Two blocks were used for each shot to capture the entire path of the projectile as it moved through the gelatin (Fig. 4).

The M-16A2 rifle produced a consistently higher muzzle velocity (3,155 � 23.6 ft/s vs. 2,848 � 31.5 ft/s; p

Discussion

Wound ballistics is the science that evaluates the pathophysiology and outcomes of wounds created by missiles. The field encompasses not only how a wound is formed but also the epidemiology, clinical course, and outcome of penetrating trauma resulting from bullets or exploding munitions.5-9 It is important for military medical personnel to understand the pathophysiology of any injury that they might be required to treat. Previous studies using the wound profile method have allowed scientists to reliably predict a firearm’s effects in soft tissue.2″4

When the M- 16Al rifle was first fielded during the Vietnam War, anecdotal reports of erratic performance in wounding were noted in nonmedical articles, although testing at a major military laboratory had noted the effectiveness of the M- 16Al rifle in comparison with the standard rifle, the M- 14. The M- 14 fired a 7.62-mm, 9.7-g bullet at a muzzle velocity of 860 m/s. In contrast, the M- 16Al rifle fired a M- 193 bullet that weighed 3.6 g and was fired at a muzzle velocity of -940 m/s.6 Diamond and Rich7 evaluated the wounds of casualties who sustained wounds from the M- 16Al rifle with the M- 193 bullet and found that the projectiles fragmented more frequently than did bullets used by the older 7.62-mm rifle.

Early medical reports noted variable wounds produced by the M- 16Al rifle in casualties. Some wounds appeared as “throughand-through” bullet wounds with relatively little soft tissue disruption, whereas other wounds showed greater tissue disruption and bullet fragmentation, even in soft tissue only. This variable appearance was later attributed to projectile fragmentation. When the projectile broke in soft tissue, greater tissue disruption occurred. Not all bullets broke up when fired into tissue, however, which accounted for less tissue damage sometimes seen with the rifle.7

The wound profile technique is used to demonstrate the amount of tissue disruption that may occur as a projectile passes through the tissue. The use of 10% ordnance gelatin in this way is most closely related to skeletal muscle in the appearance of tissue disruption.2″4 Other firearms have been tested by using the wound profile method. In comparison with the M-16A2 rifle with M-855 arnmunition, the AK-47 rifle with Yugoslavian ammunition produces less soft tissue disruption over the first 20 to 25 cm and penetrates farther. Most significantly, the projectile does not fragment. The more modern Soviet rifle, the AK- 74, fires a 3.4-g, 5.45-mm projectile that is less stable in tissue and creates a much shorter neck length. The AK- 74 projectile also does not fragment in soft tissue.6

The results from the present study show that, with shortening of the barrel, a decrease in the average muzzle velocity was seen in a comparison of the M-16A2 rifle and the M-4 carbine. The decreased muzzle velocity had several effects on the projectile-tissue interaction. The projectiles fragmented less (not significantly), which in turn allowed larger projectile fragments to continue forward in the tissue simulant, thus increasing the penetration distance seen with the tissue simulant. There is a reciprocal relationship between the amount of deformation or fragmentation that occurs and the amount of penetration that occurs in tissue. There was not a significant difference in the degree of bullet fragmentation in a comparison of the two arms, although the fragments were spread over a greater area of gelatin with the M- 1 6A2 rifle. Because projectile velocity decreases the farther the projectile moves from the weapon, the effects produced by the M-4 carbine may be seen at longer ranges with the M-16A2 rifle.

A limitation of the present study is the use of 10% (by weight) ordnance gelatin to simulate tissue. Comparison of ordnance gelatin with actual tissue has been performed to validate this material as an approximation of human tissue.2-4,10

It is important for medical personnel to understand the factors involved in the production of a wound to best care for patients who receive those wounds. Currently, U.S. medical personnel are treating both wounded U.S. soldiers and citizens of Iraq and Afghanistan who have wounds made from the M- 16 series of rifles.

References

1. Fackler ML, Dougherty PJ: Theodor Kocher and the scientific foundation of wound ballistics. Surg Gynecol Obstet 1991; 172: 153-60.

2. Fackler ML, Malinowski JA: The wound profile: a visual method for quantifying gunshot wound components. J Trauma 1985; 25: 522-9.

3. Fackler ML, Surinchak JS, Malinowski JA, Bowen RE: Bullet fragmentation: a major cause of bullet disruption. J Trauma 1984; 24: 35-9.

4. Fackler ML, Surinchak JS, Malinowski JA, Bowen RE: Wounding potential of the Russian AK-74 assault rifle. J Trauma 1984; 24: 263-6.

5. Fackler ML: Wound ballistics. JAMA 1988; 259: 2730-6.

6. Fackler ML: Wounding patterns of military rifle bullets. Int Defense Rev 1989; 22: 59-64.