Developing a Database through the Analyzation and Comparison of Cartridge Casings Fired from Unknown and Known Firearms

Used cartridge casings are convenient in criminal investigations to trace firearms back to the spent casing found at a scene. Using class characteristic toolmarks found on these casings including headstamp, firing pin impressions, breechface marks, case design, head type, color, and measurements of the neck, body, and head can be useful in eliminating unrelated firearms and narrowing it down to a group of possible firearms. Individual characteristic toolmarks are more exclusive by narrowing it down to one specific firearm by matching striation marks found on the body of the cartridge casing to the grooves on the inside of a firearm's barrel. Hundreds of casings fired from unknown firearms were donated along with samples fired from known firearms from the Liberty Gun Range to serve as controls. These samples were then measured with a caliper and analyzed under a comparison microscope. A database was created to document class and individual characteristics for further comparison research to be continued. Unknown firearm samples were compared to known firearm samples for comparison purposes within criminal investigations. It was concluded that class characteristics found on these cartridge casings generate a narrower search for matched firearms. Inconsistencies in breechface marks, firing pin shapes, firing pin marks, and extractor/ejector marks among two casings of interest propose that they came from different firearms. If both casings were found at the same crime scene, this suggests there was more than one shooter at the scene. Individual characteristics generate even narrower searches, as unique striation marks trace back to an individual firearm. Each cartridge casing that comes from the same firearm will have similar if not identical striation marks. Certain striation marks will present themselves in the same way in each casing that comes from that firearm, building a strong case for the origins of that cartridge.