Gunshot residue (GSR) consists of burnt and unburnt powder particles, primer components (lead, barium, and antimony or other elements), and particles from the bullet, firearm, and cartridge case (16,159,215,216).
The detection of GSR can determine whether an individual fired a gun. GSR can escape from the muzzle end or breeches and blow onto the hand in contact or in close proximity to the firearm (159,215-218). Both hands should be tested (22). Long arms tend not to deposit as much residue on the hands as handguns (216). GSR can be on the palm or back of the firing hand or nonfiring hand used to steady the end of the muzzle (103,215,216). Primer residue can be transferred to the palm if a recently fired handgun is picked up and moved or the wound area is clutched (63,215,216). GSR can determine whether a hole on the skin and clothing is an entry (132,215). GSR can indicate firing distance. Residue (barium, antimony) has been observed on targets 3 to 4 ft (about 1 m) away depending on the type and caliber of pistol and revolver (219).
Detection of GSR is by inorganic analysis using flameless atomic absorption spectrometry or particle analysis (lead, barium, antimony) using scanning electron microscopy/energy-dispersive X-ray (16,159,215,216,220). Material is collected by swabs, wipings, or tapelifts from the hands (16,159,215,216). The best success is with dry clean hands protected by paper bags (Fig. 31). Analysis can be done on blood-spattered hands (221).
One study showed a GSR detection rate of 44% with revolvers and 24% for pistols (95). Another study showed that 38% of all suicides had a positive reaction on the shooting and nonshooting hands (221). The frequencies were 50 and 29%, respectively, when .22-caliber revolvers and pistols were excluded. Other studies also have shown a low detection rate with .22-caliber pistols/revolvers (see Heading 9 and refs. 63 and 221). The overall detection rate rose to 50% if more than one shot was fired. With rifles and shotguns, residue is almost never detected on the firing hand, but can be found on the nonfiring hand that steadied the end of the muzzle (16). Analysis by flameless atomic absorption spectrometry can detect trace metals deposited at close range, which is useful if there is a wound edge altered by drying or decomposition, a period of survival, or interposed clothing (159).
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