Formation of Gunshot Residues

Abstract

Abstract Scanning electron microscopy combined with energy dispersive X-ray analysis (SEM-EDX) was used to determine new structural criteria to further substantiate the view that gunshot residue (GSR) particles have a characteristic structure. Because GSR particles are formed by rapid cooling from extreme temperatures and high pressures, they should contain features of condensates not only on their surfaces, but also within their interiors. Both the surfaces and the cross sections of GSR were examined for X-ray mapping of elements and for topographic analysis. Vaporized lead, antimony, and barium may condense uniformly and concurrently, or irregularly and discontinuously, or as a layer of lead around a nucleus of barium and antimony. These three modes of GSR formation may correspond to the equilibrium state, the increasing temperature state, and the decreasing temperature state of the explosion gas mixture of the priming compound. Most GSR smaller than 10 $#X3BCm are formed as droplets at equilibrium. Larger spheres grow by coalescence of the smaller droplets. These residues pass through various metastable forms and then freeze. Only a few semisolid spheroids of barium and antimony may capture lead vapors of the etched bullet and burnt residues, and these appear as “peeled oranges.”