The analysis of primer mixtures and gunshot residues using scanning electron microscopy/energy dispersive X-ray analysis

Abstract

Although the analysis of GSR using SEM/EDX has been thoroughly studied, no literature on the SEM/EDX analysis of primer mixtures of center-fired cartridges has been reported. Thus, not only GSR but also primer mixtures generated from both reference cartridges and confiscated illegal cartridges were analyzed in this work. The aim of this work is to obtain elemental composition data of primer mixtures of handgun cartridges frequently encountered in Taiwan and to provide procedures for identifying cartridge used in criminal activities through elemental analysis of GSR and primer mixtures of suspected cartridge. Twenty-five kinds of cartridges with noncorrosive primers or lead-free primers were disassembled or test-fired to collect primer mixtures or GSR, respectively. Bullet and propellants of unfired ammunition were removed, the cartridge case was deprimed, and primer mixtures were then recovered. Gunshot residue samples were collected from shooter's hand, spent cartridge case, and target surface after test firing. Both primer mixture and GSR samples were then subjected to SEM/EDX analysis. The results revealed that all of the noncorrosive primer mixtures and GSR generated from cartridges with these primers contained unique elemental composition of lead (Pb), barium (Ba), and antimony (Sb). Only Ba and Sb were detected in two kinds of lead-free primer mixtures and GSR generated from cartridges with these primers, where none of Pb, Ba, and Sb were detected in samples from the other four kinds of lead-free cartridges. Characteristic elements of Pb, Ba, and Sb were detected in all primer and GSR samples collected from illegal cartridges and were not detected in samples from police duty cartridges. These results indicated that lead-free cartridges have not yet been used by criminals in Taiwan. The significant elemental difference between GSRs from different sources is especially useful in identifying possible shooter while the fired bullet is missing.