Trace Metal Detection of Inorganic Gun-Shot Residue of 5.32 INSAS Firearms using ICP-OES and Statistical Approach

Abstract

Gunshot residues is important analysis for identifying the type of firearms and ammunitions. Organic residues fades away and inorganic residues is next analytical possibility like lead free bullets. The major challenge is detection with non-destructive analysis due to trace levels and destructive analysis like acid digestion coupled inductively coupled optical emission spectroscopy able to detect trace levels from bullet casing, firearms and explosives during the shots. This was experimented with firearms of INSAS and 5.56 mm ammunitions in various distances from 0 to 300 cm fired with single shot. The GSR substrate collected, stored and analysed for visual photography to understand the bullet hole intact. The analysis found the average hole diameter was 1.22 ± 0.16 mm via photography, which was similar to other firearms. The gun powder and GSR substrate elements has no relation due to matrice non-corrected for ammunition. Still, the study succeeded by correcting the matrices of GSR substrate found with the help of statistical approach (Spearman correlation and principal component analysis). The possible signature for this ammunition were Pb, Cu, Fe, Ni, Zn, Ba, B, Sr, Ti, Mn and Al. Cu and Pb was observed upto 120 and 60 cm with possible trend on distances fired. Using Pb and Cu ratios the distance was regressed upto 62 and 63% for both matrices approach upto 105 cm. In the real scenario, collecting the substrate away from GSR might be useful for matrice correction in ballistics distance approximation.