Time since Discharge of Spent Cartridges

Abstract

Abstract A method for estimation of the time since discharge of spent cartridges is presented. This method is based on SPME (Solid Phase Microextraction) sampling from the atmosphere inside cartridges. Either naphthalene or an unidentified compound designated as the TEA2-compound were detected in most of the cartridges. These combustion products are the same as those measured in firearm barrels, but in cartridges the detected amounts are lower. The estimation of time since discharge is based on the rate of escape of the volatile combustion compounds from the cartridge as a function of time. Three categories of cartridges were studied separately—shotgun shells, cartridges from sporting rifles, and cartridges from pistols/revolvers. For shotgun shells the decay of the naphthalene peak is measured. At room temperature, naphthalene is detectable in shotgun cartridges for 2–3 weeks after the discharge. In cartridges from sporting rifles, only the TEA2-peak is detectable and observable for about 2 weeks after the discharge. The technique presented failed to detect any combustion product in pistol/revolver cartridges, with the exception of longer cartridges, such as Magnum and in small caliber cartridges (caliber .22) where the TEA2-peak was observed for several days after the discharge. Nitroglycerin (NG) was detectable in cartridges from some manufacturers, but the reproducibility of its detection was rather poor. Moreover the decay of NG was too slow at temperatures below room temperature. The repetitive SPME sampling did not disturb the system. Attempts to prevent the volatile compound from escaping from cartridges was unsuccessful. Some experiments were performed with cartridges stored outdoors, exposed to wind, rain, and snow.