Evaluation of barrel wear caused by polymer coated bullets

Abstract

Forensic firearm analysis resides on the principle that each firearm is capable of imparting individual characteristics on ammunition components. Individual characteristics can be used to link a bullet or cartridge case back to the firearm which fired it. Bullets acquire these markings from the interior features of the barrel, which are subject to change over time due to wear caused by repeated firing and possible damage. Among various ammunition available, polymer-coated ammunition, such as Federal Total Synthetic Jacket (TSJ) ammunition, has recently gained popularity for its potential to reduce lead exposure and firearm fouling. However, while existing literature documents barrel wear caused by traditional ammunition, the forensic implications of TSJ ammunition remain under-researched, particularly regarding its impact on barrel wear and the visibility of individual toolmarks used for firearm identification. The goal of this study was to determine whether Federal Premium’s Total Synthetic Jacket (TSJ) ammunition causes less barrel wear and degradation of individual characteristics compared to Full Metal Jacket (FMJ) ammunition over the course of 500 shots. Two Glock 19 Gen5 caliber 9mm Luger pistols equipped with Glock Marksman Barrels (GMBs) were used, one firing exclusively FMJ bullets (known as the control), and the other firing TSJ rounds while also firing an FMJ round every 10th shot (known as the experimental). Of 1000 fired bullets, 102 were collected for analysis. Three-dimensional scans of the land engraved areas (LEAs) were captured using the Cadre Forensics TopMatch-3D system. The Congruent Matching Profile Segments (CMPS) algorithm, integrated into the Cadre software, was employed to compare the LEAs quantitatively. A total of 612 LEA scans were collected and examined. Results have indicated that the polymer-coated TSJ bullets led to increased wear of the barrel surface, significantly reducing the clarity and frequency of striated toolmarks over successive firings. In contrast, FMJ rounds maintained a higher level of individual characteristic retention. The Kwiatkowski Phillips Schmidt Shin (KPSS) time series test was used to test the stationarity in the dataset. Results suggest that TSJ ammunition may contribute to increased barrel wear and does have a significant effect on the clarity and frequency of striated toolmarks across successive firings. In contrast, FMJ rounds do contribute to barrel wear, while also maintaining striated toolmarks necessary for forensic comparison.