Computed tomography and 3D visualization in forensic shooting distance estimation - A ballistic gelatine pilot study

Accurate estimation of shooting distance is one of the main aspects in forensic gunshot case reconstruction. Reliable methods to estimate shooting distance are thus important for forensic practitioners. In this pilot study we test how computed tomography (CT) based evaluation of bullet cavitation could potentially be utilized to differentiate shooting distance. To conduct our study, we utilized ballistic gelatine blocks as a soft tissue simulant. Test shooting was performed from two distances, 20 and 100 m. Four expanding monolithic bullets were used all in 0.30 caliber (Barnes TTSX, Sako Blade, Norma Ecostrike, Lapua Naturalis). The gelatine blocks were CT-scanned after the experiment. The scans were processed and segmented using an open-source 3D Slicer software to provide a 3D reconstruction of the cavitation and obtain numerical cavitation parameters (total volume and surface area of cavitation; maximum crack diameter; location of maximum cavitation). Our results indicated that all four bullets had distinct terminal ballistic performance. This could be detected from the bullet parameters such as maximum diameter and also from the pattern of cavitation. Shooting distance had a consistent, measurable association with bullet diameter and surface area of the gelatine cavity in all four bullets. Our preliminary pilot study underscores the potential of CT in the comprehensive analysis of gelatine cavitation in terminal ballistics. Our results suggest that it would be essential to know exact bullet type when shooting distance is estimated from terminal ballistic findings.