19th INTERPOL International Forensic Science Managers Symposium Lyon, France

Although the correspondence of features in the firing pin aperture shear mark and the breechface impression led to an identification, the features in the firing pin impression were completely different between the test shots and the seized cartridge cases. [...] The marks resulting from the barrel extension lugs of the M-16 assault rifle are formed on the neck of the cartridge case during the extraction and ejection cycle. [...] The author discusses that resulting evidential strength is influenced by the comparison results, but also by the age of the ammunition, by how common the ammunition is and by the explanation offered by the suspect about the acquisition of the ammunition. [...] The soiled and oxidized ammunition is examined and the authors conclude that the chemical composition of the ammunition remained unchanged, but that the ammunition became ineffective due to absorption of moisture by the primer [65]. [...] Combining long shutter times (enabling the CSI to walk the reflector card down the length of the trajectory beam, and a diaphragm setting of f/22 resulted in photographs of the trajectory beam without obvious ghosting of the reflective card or CSI [135].