The study used more than 500 rounds of commercially available ammunition and 6 different types of handguns to examine 17 gunshot residue specimens and 19 reference specimens. The individual particle x-ray composition was determined for 12 different elements. Results revealed that elemental composition of gunshot residue particles was highly variable but consistent with compounds mixed into or associated with a barium oxide matrix. Gunshot residue that was present in a specimen could be adequately characterized with automated procedures in less than an hour by restricting analyses to features larger than 1 micrograms. A higher-resolution particle search was required in clean samples to avoid reporting false negatives. Careful control of the back-scattered electron signal strength threshold, by reference to a standard, was needed to ensure both time-efficient and accurate analyses. Finally, samples collected from non-shooting subjects, active in a physical setting that contained firearms discharge residue, were easily contaminated by sub-micron gunshot residue particles. Photographs, tables, figure, and 18 references (Author abstract modified)