Experimental wound ballistic study to understand biomechanical differences in gunshot wounds from various bullets and...

Previous wound ballistics studies have examined the bullet's behavior while perforating gelatin. However, there has been limited attention to analyzing effects of bullet mass and energy transfer relating to magnitude and depth of the injurious temporary cavity with its clinical implications. Twenty-one bullets were fired into validated 20% synthetic ballistic gelatin with pressure transducers and high-speed videography. Bullet velocities, energy transfer, and maximum temporary cavities were calculated. Generalized linear models were developed to assess significant effects of bullet size, mass, and impact velocity for magnitude and depth of maximum pressure and temporary cavity diameter. A porcine femur was embedded in gelatin to demonstrate fracturing potential of the temporary cavity from an AR-15 5.56 NATO projectile. Maximum temporary cavity diameter and energy transferred expressed an exponential relationship (R² = 0.91). Bullet caliber (p = 0.039), bullet mass (p = 0.008), and impact velocity (p < 0.001) were significant predictors of maximum temporary cavity diameter. Bullet mass significantly influenced the depth of the maximum temporary cavity (p = 0.006), which expressed a moderate linear relationship (R² = 0.55). Substantially greater maximum pressure was observed in 30 - 06 caliber rounds from bolt action rifles and one fragmented AR-15 5.56 NATO projectile. The temporary cavity from an AR-15 5.56 NATO projectile was 17.1 cm in diameter and resulted in a complete middle diaphyseal wedge fracture of the femur with a bullet path 8.1 cm from the bone. Knowledge of relative magnitudes and locations of maximum temporary cavities may aid emergency physicians and trauma surgeons in identifying potential damage from gunshot wounds.