The scarcity of mercury in discharge residue particles from mercury-containing ammunition was investigated. It was found that 86% of the mercury was vaporized after discharge, mainly via the muzzle, 88% of which was not detectable by SEM. Of the 0.16% exiting via the breech, only approximately 40% was detectable by SEM. Only a small proportion of this was deposited on the firer. The recovered mercury did not make a significant contribution to the elemental composition of the discharge residue particles. The rate of loss of mercury from the spent cartridge case was also examined but was found to be of no practical value in estimating time of discharge.