Quantitative assessment of barrel wear from solid copper bullets

Forensic firearm and toolmark identification is based on the principle that firearms possess and impart individual characteristics on fired ammunition, which can be used to identify a bullet back to the barrel from which it was fired. However, these characteristics may change due to use, presenting challenges for firearm examiners. The goal of this research was to determine how solid copper bullets affect barrel-rifling characteristics after firing 500 rounds through a new Glock 19 Gen 5 pistol with a Glock Marksman Barrel (GMB). Of the 500 bullets, the first 10, last 10, and every tenth in-between were collected in consecutive order for a total of 68 bullets. Three-dimensional (3D) scans of the land engraved areas (LEAs) were generated using the Cadre Forensics Versa system. Cadre Forensics' implementation of the Congruent Matching Profile Segments (CMPS) algorithm was used to compare the linear striation profiles of the LEAs. These data were analyzed using the Kwiatkowski-Phillips-Schmidt-Shin (KPSS) time series test, resulting in a statistically significant decreasing trend (p < 0.01) across CMPS scores from bullet 1 to bullet 500. Based on the algorithm scores and visual comparisons of the LEA scans, this study demonstrated that solid copper bullets eroded barrel characteristics over 500 shots to where an identification likely would not be made when comparing bullet 1 to bullet 500. These results indicate that firearm examiners need to consider the time between a shooting event and firearm recovery to account for potential changes to barrel characteristics that may impact bullet comparison interpretation.