Elemental analysis of primer mixtures and gunshot residues from handgun cartridges commonly encountered in Taiwan

Inorganic gunshot residues (GSR) can arise from each component of the fired cartridge and GSR deposits inside the barrel from previous shootings. This work focused on the analysis of primer mixtures that yield GSR-unique particles. Primer mixtures and gunshot residues from 25 kinds of cartridges were recovered and subjected to scanning electron microscopy/ energy dispersive X-ray analysis to obtain morphological and compositional data. The results revealed that 17 kinds of cartridges using non-corrosive primer that contained lead styphnate, barium nitrate, and antimony sulfide. The identity of lead styphnate was confirmed by its distinctively shaped rhombic crystals. In addition to Pb, Sb, Ba, and S, other elements such as Al, Ca, Si, and P were also detected in non-corrosive primers. Seven kinds of cartridges were found to use lead-free primers, where two of them contained Sb, Ba, and S. Major elements detected in the other lead-free primers were common elements such as K, Mg, and Zn except that strontium was detected in one primer and zirconium was detected in another. Major elements detected in GSR particles were generally in accordance with those of their respective primers. Other minor elements from various sources were also detected. The Pb-Sb-Ba unique particles were detected in all GSR samples from cartridges using non-corrosive primer with the exception of S&B 9 mm cartridge where Pb-Ba-Sn particles were detected. The elements detected in particles from lead-free cartridges were not as characteristic as typical GSR except that Sb-Ba were detected in GSR from two lead-free cartridges. The Sb-Ba particles were regarded as GSR specific when their spherical morphology was simultaneously taken into account. Gunshot residue particles from gun hands and targets were mainly spheroidal in shape with a diameter smaller than 10 μm. Gunshot residues from spent cases were usually irregular in shape and present as flakes or aggregated mass sometimes bigger than 100 μm. The elemental composition of GSR was found to be primer type dependent. To reach a meaningful interpretation of GSR analysis results, the comparison of suspected GSR particles with known GSR of the cartridge used is even more important than the uniqueness of the particles’ elemental composition. Gunshot residues recovered from the spent case, the fired bullet, and the bullet hole could be used for comparison. If the firearm and the cartridge used in the crime are available, primer mixtures and GSR from test firings should also be analyzed.