Effect of mounting a sound suppressor on distribution and total amount of inorganic gunshot residue on targets

Sound suppressors critically modify barrel overall length and ballistic performances of hosting guns and are therefore expected to influence the patterns of the plumes of gunshot residues (GSR) reaching the targets. Despite the forensic interest, in recent years, a single paper was published on the variations induced by the use of a suppressor in the spatial distribution of visible soot clouds on close targets and in the number of a few selected classes of GSR particles detected by scanning electron microscopy. A different approach, based on x-ray fluorescence (XRF) and inductively coupled plasma-optical emission (ICP-OES) spectroscopies, that points to most of the metallic elements ejected from the barrel, is suggested here. The confirmed effect of a sound suppressor up to a distance of 20 cm is to gather the cone of particles reaching the target. Despite this pattern modification, the global concentrations of the ammunition-related elements of interest (Pb, Ba, Sb, Cu) on targets cannot be considered significant (i.e., with 95% confidence) reduced by the use of a suppressor, due to the high intra-specimen and inter-specimen ICP-OES data dispersions. Differently, the hypothesis of a role of homemade suppressors in enriching GSR populations in Fe is supported by our results. The presence of iron is indeed the only indication of the actual use of a suppressor, a piece of information that is useful for the correct interpretation of the lead patterns visualized on targets for muzzle-to-target determination.