Date of Graduation
Eberly College of Arts and Sciences
Forensic and Investigative Science
Keith B Morris
Firearms evidence plays a vital role in shooting incident investigations. Included in this type of evidence is the comparison of fired cartridge casings. The evaluation of cartridge casings can inform investigators as to the number of firearms used in an incident. This evaluation includes the observation of breech face impressions imparted on the cartridge casing by the firearm. The comparison of these markings can assist investigators in the apprehension of perpetrators. However, the quality of these impressions may vary based on the pressures generated within a single system during firing leading to the appearance of multiple firearms being involved. Investigation into the differences in breech face markings generated by a single firearm should be conducted.;In this study, .38 Special and .357 Magnum ammunition was reloaded to ensure variables were kept constant between each cartridge while varying the powder type and weight. Pressures generated during firing were recorded using the PressureTrace II(TM) system and muzzle velocities were measured using a MagnetoSpeed ballistic chronograph. The PressureTrace II(TM) system allowed for plots of pressure against time to be generated for each firing repetition. Each fired cartridge case was then entered into the Integrated Ballistic Identification System (IBISRTM) allowing breech face and firing pin correlation scores between the cartridge cases to be generated. Correlation scores between the cartridge cases were then assessed for differences in breech face and firing pin scores. It was found that cartridges with greater differences between their charge weights and pressure gave lower average breech face scores while cartridges with more similar charge weights and pressures gave higher average breech face scores. However, firing pin scores showed less variation based on these variables.
Hamilton, James A., "Effect of Chamber Pressure on the Quality of Breech Face and Firing Pin Impressions" (2017). Graduate Theses, Dissertations, and Problem Reports. 5743.