Date of Graduation
Eberly College of Arts and Sciences
Forensic and Investigative Science
A major activity in firearms examination is the comparison of cartridge cases. In a crime scene where a firearm was discharged, it is very common to find cartridge cases littering the scene. Firearms examiners examine these cartridge cases along with test fired cartridge cases from the suspected firearm. They inspect the firearm to ensure that it is safe and in working condition before conducting test fires. These test fires are then compared to the submitted evidence. Comparison microscopes are used to visualize the impressions left on the cartridge case from the firing process. When comparing evidence to a known test fire, the examiner looks for similarities and differences in the breech face impressions, firing pin impression, and other markings by looking for any individual characteristics. Based on previous research, it is known that variability in cartridge case impressions exists from one shot to the next. Most studies do not mention the rate of fire at which test cartridge cases were collected. It was thus hypothesized that significant differences would be observed in cartridge cases fired by the same firearm at various rates of fire, which was supported by this research. The differences were measured using the Congruent Matching Cells (CMC) algorithm. Three (3) semi-automatic firearms were used for this study. Cartridge cases were collected using three (3) rates of fire (Low, Medium, High) for each firearm. For each rate of fire, fifteen (15) cartridges were discharged. An audio recorder was used to collect recordings of the discharge of the cartridges. The recordings were used to estimate the rate of fire. After collection, all cartridge cases were scanned using a Sensofar S Neox optical profiler confocal microscope. The scans were cropped to only include the breech face impressions and compared using the CMC algorithm. Data analysis were performed utilizing the analysis of variance (ANOVA) methods along with the Tukey honest significant difference (Tukey HSD) for the post hoc test as well as the non-parametric Kruskal-Wallis method and the Dunn test.
Trimble, Kayla Ann, "Analysis of the Effect of Rate of Fire on the Reproducibility of Breech Face Impressions" (2023). Graduate Theses, Dissertations, and Problem Reports. 12068.
Available for download on Thursday, July 25, 2024