Objective evaluation of consecutively manufactured Glock Marksman Barrels using <scp>EvoFinder</scp> ®

Glock Inc. introduced the Glock Marksman Barrels (GMBs) for their fifth-generation production model, in which they incorporated an additional rail component to their existing polygonal rifling process. This addition has resulted in debate among firearm examiners regarding its effectiveness for identifications. This study answers important questions regarding their manufacture, the presence of subclass, how the resulting striations differ barrel to barrel, and if the addition of the rail component offers a benefit or hindrance for examiners during microscopic comparisons. Production and manufacturing information was ascertained via a trip to the Glock factory in Smyrna, GA. Glock engineers provided key information on mandrel fabrication and barrel rifling manufacture. Microscopic evaluation of casts obtained from unfired, consecutively manufactured GMBs revealed repeating patterns among sections of each rail. This is a result of mandrel manufacturing practices resulting in subclass carryover during hammer forging. The tool marked surfaces of GMB bullets, 12 fired from each of 10 consecutively manufactured barrels, were scanned into the EvoFinder® system. An objective evaluation utilized the system's algorithm to determine if each fired bullet could be properly assigned to its original barrel, regardless of the region used. Results demonstrate that inclusion of N-max as a criterion for comparison, in the form of a total score calculation, allowed for complete separation of KM and KNM distributions for additional regions. Furthermore, examiners tested with sets prepared from the same bullets, where the LEAs and GEAs were concealed, found no indication that subclass carryover on the rails would result in false positives.