In any well-funded laboratory, chemical spot tests for bullet entry/exit hole determination are generally a thing of the past. The vast majority of chemical tests used for such purposes can be carried out with a far higher degree of precision by use of the SEM.
Range of firing estimations are normally carried out by visually estimating the density of partially burnt propellant particles on the surface being examined. In handguns, the maximum range that these particles can be seen, even when using a microscope, is about 24 in. (60 cm). The presence of primer discharge residues can, however, be picked up with a SEM at ranges of 15 ft (5 m) or more.
The process is very laborious and involves taking tapings from control firings at a set distance, usually 4 in. (10 cm) from the bullet hole. From these tapings, a GSR particle density is calculated for each range. These particle densities are then compared to tapings taken from the garment in question and a range of firing estimation obtained.
As the GSR distribution will be different for each type of ammunition/barrel length combination, it is essential that these parameters are known before range of fire estimations can be calculated from the GSR particle density distribution tables. This technique does, however, enable range of fire estimations to be made at distances which cannot be accomplished by any other method.
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