Gunshot residue from lead-free ammunition: Inorganic vs. organic analytical techniques

Within the last years, there has been a significant number of patents granted for lead-free and non-toxic primer mixes and car- tridges manufacturers are increasing the number of products having a non-toxic primer mix. Despite this trend there are a few papers about the analysis of gunshot residue (GSR) produced by non-toxic primed ammunition with Scanning Electron Microscopy (SEM). The aim of the present research was to analyse the GSR produced by the leadfree cartridges 9 mm Luger on the market. Samples were taken from the inside of spent cartridge cases, from targets and from hands of shooters and were analysed with a variable pressure (VP) SEM. The VP SEM permitted the direct analysis of cotton or paper targets. Particles were located using the Backscattered Electron (BSE) images and then elemental composition were deter- mined recording EDX spectra. Automatic search were performed on stubs used for sampling from spent cases and from shooters’ hands in test firings. The differences between the population of par- ticles found inside the cartridge cases and the population sampled on hands or on targets suggested to study the effect of previous shots with lead primed ammunition on tests where lead-free ammu- nition where used. Examples of some exceptional compositions of gunshot residue particles, formed by using different types of am- munition with traditional primers in the same firearm, were already published. We examined the particles formed shooting traditional primed cartridges folowed by lead-free primers. Twenty rounds of cartridges containig lead, antimony and barium in the primer where shot on separate targets. The GSR around the bullet hole (bullet wipe) and at a distance of 1 cm from the hole where sampled using double-side adhesive coated aluminum stubs (the tape-lift method) on the 20th target. The same weapon (semiautomatic pistol) was then used to shot leadfree ammuniton on separate targets. Samples were taken every 5 shots to examine the variation of the chemical composition of particles. The population of particles collected on targets showed significant changings. These findings suggest to in- clude the search for different residue in all the cases where lead-free cartridges were used, due to the poor evidential value of analytical results obtained using only SEM. A complete analytical procedure to be used in these cases is illustrated.