LAUSR

In Australia, shotguns feature in criminal activity and suicide shootings relatively frequently. However, compared to studies dealing with GSR originating from rifled firearms, those dealing with residues originating from shotguns are rare. The purpose of the research described in this article was to specifically characterize particle populations ejected from shotguns, and especially populations produced when ammunition containing steel shot was used, as it was expected that the high levels of iron likely to be produced during discharge may complicate GSR evidence evaluation. The expected high numbers of iron particles in GSR ejected from the muzzle of a shotgun during discharge of cartridges loaded with steel shot were not detected. The inevitable conclusion of that finding - that metal from the shot does not contribute to GSR ejected from the muzzle of a shotgun - was confirmed when practically no particles containing zinc were detected when cartridges loaded with zinc plated shot were fired. It is suggested that the shot-cup in the ammunition was very effective at preventing the formation of GSR particles from the shot. In contrast to those findings, high numbers of iron particles were detected in GSR ejected from the breech of a shotgun when ammunition loaded with steel shot was fired. However, when ammunition loaded with bismuth or tungsten shot was fired, the levels of tungsten and bismuth particles ejected were very low but high numbers of iron particles were still detected. It is suggested that the firing mechanism in the gun itself, rather than the ammunition used, is responsible for the abundance of iron detected in GSR ejected from the breech. Despite the presence of iron in shotgun GSR, typical primer-derived residues (containing any or all of the elements lead, barium and antimony) were detected in residues ejected from the muzzle and the breech therefore evidence evaluation is relatively straightforward.