Terminal ballistics of the Russian AK 74 assault rifle: Two wounded patients and experimental findings

Military Medicine, Dec 2001 by Korac, Zelimir

The Russian AK 74 assault rifle was introduced in the mid 1970s as the successor of the older AK 47 rifle. A cross-section of the AK 74 5.45 x 39 mm missile is shown in Figure 6. The bullet has a gilding metal envelope, and inside it there is a 15-mm-long mild steel core coated with lead. The bottom of the steel core lies at the bottom of the metal envelope. On the tip of the steel core, there is a 3-mm lead plug, and in front of that a 5-mm-long hollow space displacing the missile's center of gravity backward and making the missile more prone to tumbling after collision with the target. Small variations in the size of the empty space in the tip of the bullet may be causing the unpredictable path of each missile.

The gelatin blocks we used were 47 cm long, and all bullets exited the blocks, but only six of them exited through their back face. This finding is in correlation with a report by Fackler et al. 8 who found two of three bullets to exit through the upper or lateral faces of the block.

We believe that the differences between our results and those of Fackler et al. cannot be explained solely by possible differences in the physical properties of the gelatin blocks or different shooting ranges (3 m vs. 8.5 m). Potential differences in bullet design have to be considered as well.

Our gelatin blocks were not calibrated. According to some authors, the calibration of the blocks is essential for reproducibility of terminal ballistic studies. However, significant variations exist in the composition and preparation of gelatin blocks reported by different authors. In studies by U.S. authors, gelatin blocks are usually made of ordnance gelatin (type 250 A, Kind and Knox Co., Sioux City, Iowa) in 10%5,6,10,11 or 20%12-15 (wow) aqueous solutions. European researchers use blocks made of different types of gelatin in various ratios and at various temperatures. Gelatins are usually graded by jelly strength, which is expressed as "Bloom strength," "Bloom rating," or "Bloom number," and this characteristic is, according to some reports, even more important than temperature and concentration. 16 We used an aqueous gelatin solution that was 20% by volume and 15.3% by weight.17 According to the subjective evaluation of the blocks performed by the surgeons involved in the team, the consistency of the gelatin after the cooling approximated the consistency of human striated muscle.

The clinical significance of the absence of double temporary cavities is limited to very long wound channels. The loss of stability of our missiles occurred at somewhat longer penetration distances than in experiments by Fackler et al.7 (Fig. 1). Possible reasons are differences in bullet design and in physical characteristics of the gelatin blocks. Also, it must be remembered that wound profiles are averages and not exact prescriptions of wound patterns to the nearest centimeter.

Minimal soft tissue damage in our patients confirms the fact that highly elastic tissues such as skin and muscle are resistant to forces that appear in terminal ballistic phenomena. 18 These tissues are soft and flexible, and they possess the physical properties of good shock absorbers. We also confirmed the fording of Fackler and Burkhalter that even the highest-velocity military bullets may cause only minimal disruption in the initial 12 cm of tissue penetration.19 We believe that one should be conservative in the debridement of this zone of such wounds. Unpredictable missile behavior regarding the direction of its path before the appearance of significant yaw was well documented for M16 Al military rifle bullets.9 Contamination of the wound and the presence of surface material in the wound should be treated according to the established principles of war surgery. 1-4