The varying size of exit wounds from center-fire rifles as a consequence of the temporary cavity

To study the question whether and how the size and position of the temporary cavity influence the morphology and especially the size of a bullet exit wound, test shots were fired to composite models consisting of gelatine and pig soft tissue covered with skin (at the exit site). The dimensions of the composite model were determined such that the exit planes were located either at the level of the narrow channel or within the temporary cavity or behind it. The chronological sequence of wound formation and its relation to the current position of the bullet were documented by means of a high-speed camera. Test shots were fired from a distance of 10 m using 5.56 × 45 mm cartridges with full metal-jacketed pointed bullets (v ₀ ∼ 912 m/s, E ₀ ∼ 1,663 J). The study proved that the extension and position of the temporary wound cavity was decisive for the size of the exit wound: An exit plane within the cavity resulted in particularly large skin lesions, whereas the wound diameters were much smaller if the exit plane was located in front or behind the cavity. The exit hole reaches its maximum size only after the bullet has left the target synchronous to the staggered expansion of the temporary cavity.