Distribution may be defined as "the areas where FDR is deposited and the concentration in those areas." It was thought that rifles and handguns when fired in the normal manner would produce different distribution patterns on the firer, with rifles more likely to deposit FDR on the face than handguns. It was also thought that the distribution on the hands could determine whether or not the test subject had discharged or merely handled a gun. On firing a gun more residues are expected to be deposited on the back of the firing hand than on the palm.
Table 17.1 Particle Population, One Shot, Same Caliber
Total Spherical Nonspherical Powder
Cartridge Particles Pb Only Ba Only Pb, Ba Pb, Sb Pb, Sb, Ba Pb, Cu Particles Flakes
125 grain JHP 142 35 35 34 13 19 6 13 18
158 grain RNL 2,664 2,086 66 367 39 106 0 28 4
158 grain RNL 4,551 4,162 0 101 95 193 0 0 3
Although these initial distribution patterns may be correct under ideal test conditions, loss of residue during the course of normal activity and redistribution by transfer from area to area complicate the issue. With the exception of suicides and dead suspects, the initial distribution pattern will almost certainly have altered markedly between the incident and sampling, which is typically several hours after the event. In practice the circumstances of the case dictate the areas to be examined for FDR.
There are many factors that influence the initial distribution pattern and most have been mentioned when discussing the quantity of FDR deposited. This coupled with the loss of residue with time and activity, and the fact that residues are readily transferred from area to area, means that any interpretation based on distribution needs to be approached with caution. Distribution is of limited practical value, but it has been an important factor in a few unusual cases.
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