In order to improve understanding of the accuracy, reliability, and measurement validity of forensic firearm and tool mark identification, this study examined the repeatability and uniqueness of striations/impressions on cartridge casings fired in 10 consecutively manufactured 9mm Ruger slides.
The study established an error rate of less than 0.1 percent. Durability testing determined that the Ruger slides maintained their individual signatures after multiple firings. This study indicated that sufficient empirical evidence exists to support the scientific foundation of firearm and tool mark identification. Once the specter of subclass influence is eliminated, each firearm/tool produces a signature of identification (striation/impressions) that is unique to that firearm/tool. Through the examination of the individual striations/impressions, the tool mark signature can be positively identified to the firearm/tool that produced it. This research also indicates that firearm and tool mark examiners will be able to identify correctly unknown casings to the firearms that fired them when examining casings fired at different intervals through consecutively manufactured slides, using individual, unique, and repeatable striations/impressions. One semi-automatic pistol and nine additional consecutively manufactured slides were used. Consecutively manufactured slides were significant to this study because they were manufactured with the same equipment/tools, one right after the other. Even though these slides were consecutively made, their signatures should be different. Test sets included test-fired casings from each slide, as well as unknowns. Participants were firearm and tool mark examiners throughout the United States. A total of 158 test sets were distributed to laboratories in 46 States and the District of Columbia. The test sets were designed to determine an examiner's ability to correctly identify unknown cartridge casings fired from 10 consecutively manufactured Ruger slides to test-fired cartridge casings fired from the same slides. (Publisher Abstract)