The original particle classification scheme192 has been revised based on casework experience, research work on blank cartridges, and so forth, and a detailed analysis of 14 years of casework results. The particle classification scheme used in Northern Ireland since 1984 is given in Table 19.5. The indicative particles are in tentative order of decreasing significance.
The classification scheme is based on discharge residue particles from modern primed brass-cased ball ammunition. It is only applied rigidly when no other information is available. When a gun, ammunition, spent cartridge case, or bullet is recovered, it can be examined to determine elemental composition and likely discharge residue particle composition.
The classification scheme has to be flexible in order to encompass the wide range of different primer/cartridge case/propellant/bullet combinations. For example, zinc-coated steel-cased ammunition gives iron and zinc at major levels in the discharge particles; firearms with rusted barrel interiors or the use of steel jacketed bullets can produce discharge particles with iron at major level; primers containing lead hypophosphite can give discharge particles with phosphorus at major level; ammunition with black powder can produce discharge particles with potassium and sulfur at major level. Because of these and other variables the classification scheme has to be flexible.
It must be stressed that the classification scheme is intended as a general guide and is only applied rigidly when there is nothing recovered for comparison purposes.
FDR particles have been noted in a wide range of shape, size, and appearance. They all have the appearance of having condensed from a vapor or melt, namely, a three-dimensional roundness. Ragged or straight edges or corners suggest a mineral origin. The shape and appearance is particularly important in the indicative category to aid the differentiation from occupational/environmental particles. (Particles originating from the bullet/bullet jacket are sometimes encountered. These are usually identifiable and are not included in the particle classification scheme.)
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