The method is based on SPME (Solid Phase Microextraction) sampling from the atmosphere inside cartridges. Either naphthalene or an unidentified compound designated as the TEA-2 compound were detected in most of the cartridges. 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. At room temperature, naphthalene was detectable in shotgun cartridges for 2-3 weeks after the discharge. In cartridges from sporting rifles, only the TEA-2 peak was detectable and observable for about 2 weeks after the discharge. The technique 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) in which the TEA-2 peak was observed for several days after the discharge. Attempts to prevent the volatile compounds from escaping were unsuccessful. Some experiments were performed with cartridges stored outdoors, exposed to wind, rain, and snow. Figures, tables, references