Terminal ballistics of the stray bullet in soft tissue simulant –proof-of-concept

A stray bullet is a projectile that, after being fired, strikes an unintended object, such as a bystander. Accident of this kind can occur due to several reasons, such as crossfire, celebratory gunfire and sports shooting related incidents. Even though the forensic importance of such events is great, they may also present diagnostic challenges to forensic practitioners. In case of an incident involving a potential stray bullet, distinguishing between homicide and accident is important. Estimating the shooting distance can be an important part of the process as stray bullets may be lethal even from very long distances. Verifying or disproving claims regarding shooting distance may thus be among the main interests for forensic practitioners in potential stray bullet cases. In this study, we investigated whether a stray bullet strike from half a kilometer away could be distinguished from more typical shooting distances on the basis of terminal ballistic performance. To conduct our study, we utilized ballistic gelatine blocks as a soft tissue simulant. Test shooting accounted for impact velocities corresponding to 100 m and 500 m shooting distances. Two expanding monolithic bullets were used in 0.30 caliber (n = 4). After the experiment, the gelatine blocks underwent computed tomography (CT). The CT scans were analyzed using an open-source software to provide a visual 3D reconstruction of the gelatine cavitation and obtain cavitation parameters (total volume and surface area of cavitation; maximum crack diameter; location of maximum cavitation). The results of our experiments indicated that the bullets had distinct terminal ballistic performance depending on the impact velocity. Bullets simulating the impact velocity of 500 m shooting distance produced lower gelatine cavitation volume, surface area, and maximum crack diameter than the ones simulating 100 m shooting distance. Through comparative analyses performed on a case-by-case basis, CT scans may help forensic practitioners estimate the probability of a stray bullet scenario.