Accuracy of impact angle determinations from bullet holes in drywall panels

Abstract

When a bullet strikes a surface such as a drywall panel, it may perforate the material leaving a hole in the surface or it may ricochet. When multiple bullet impacts exist, for example through a wall section, the probing method allows for the trajectory of a projectile to be reconstructed. Past studies have shown that low angle impacts are subject to error when applying the probing method. Hence, this study used the probing method to examine bullet impacts in wall sections made of drywall to determine the accuracy of the angle of incidence with respect to a known firing position. To control the angle of incidence, drywall panels were positioned at different angles beginning at 90° and decreasing until the panels were at 10°. The measured angle of incidence was compared to the known angle of incidence to determine the accuracy/error. The study observed how .40 S&W caliber ammunition from four different manufacturers, interacted with drywall panels. For each ammunition type and known angle there were three replicates, for a total of 84 impacts (n = 84). It was observed that as the angle of incidence decreased, the error of the measured value increased. Measurements from panel positions at higher angles (between 60°–90°) were more accurate and precise than measurements from panels positioned at lower angles of incidence (10°–45°). The data collected in this study provides insight into the probing method and how the accuracy of measurements can be impacted while the angle of incidence decreases.