Gunshot residue

Gunshot residue (GSR), also known as cartridge discharge residue (CDR), "gunfire residue" (GFR), or firearm discharge residue (FDR), is residue deposited on the hands and clothes of someone who discharges a firearm. It is principally composed of burnt and unburnt particles from the explosive primer, the propellant—and possibly fragments of the bullet, cartridge case, and the firearm.

Law enforcement investigators test the clothing and skin of people for GSR to determine if they were near a gun when it discharged. Gunshot residue can travel over 3–5 feet (0.9–1.5 meters) from the gun. At the farthest distance, only a few trace particles may be present.

In 1971 John Boehm presented some micrographs of GSR particles found during the examination of bullet entrance holes using a scanning electron microscope. If the scanning electron microscope is equipped with an energy-dispersive X-ray spectroscopy detector, the chemical elements present in such particles, mainly lead, antimony and barium, can be identified.

In 1979 Wolten et al. proposed a classification of GSR based on composition, morphology, and size. Four compositions were considered characteristic:

The authors proposed some rules about chemical elements that could also be present in these particles.

Wallace and McQuillan published a new classification of the GSR particles in 1984. They labeled as unique particles those that contain lead, antimony, and barium, or that contain antimony and barium. Wallace and McQuillan also maintained that these particles could contain only some chemical elements.

In the latest ASTM Standard Guide for GSR analysis by Scanning Electron Microscopy/Energy Dispersive X-ray Spectrometry (SEM-EDX) particles containing lead, antimony and barium, and respecting some rules related to the morphology and to the presence of other elements are considered characteristic of GSR. The most definitive method to determine if a particle is characteristic of or consistent with GSR is by its elemental profile. An approach to the identification of particles characteristic of or consistent with GSR is to compare the elemental profile of the recovered particulate with that collected from case-specific known source items, such as the recovered weapon, Cartridge cases or victim-related items whenever necessary. This approach was called ‘‘case by case’’ by Romolo and Margot in an article published in 2001. In 2010 Dalby et al. published the latest review on the subject and concluded that the adoption of a ‘‘case by case’’ approach to GSR analysis must be seen as preferable, in agreement with Romolo and Margot.

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