Macroscopic observation of the morphological characteristics of the ammunition gunpowder.

At the present time, optical examinations are not used in routine to analyze the gunshot residues, except for the counting and the localization of particles. Indeed, the sequence of examinations often starts immediately with destructive techniques, contrary to the widely accepted law saying that we should progress from general to particular and from non-destructive to destructive and which is recommended for all the fields of forensic sciences. When a cartridge is shot, and before the projectile leaves the gun, all the powder grains should must be completely burnt; however, if this ideal case does not happen, it is possible to find unburnt and/or partially burnt gunpowder particles [H.H. Meng, R. Caddy, Gunshot residue analysis-a review, J. Forensic Sci. 42 (1997) 553-570]. The goal of this paper is to study the morphological characteristics of the powder before and after the shot, to establish if it is possible to determine which type of ammunition has been used on the basis of these characteristics. A set of 181 cartridges of different calibers was considered and various tests carried out to evaluate the technique. On the basis of the observation of the gunpowder particles found on the target, a list of potential cartridges can be established with the actually shot cartridge always found among them. It is important to underline that a maximum of eight cartridges were proposed for each experiment. Consequently, the method can be judged very discriminating. A database was then created, including information related to the morphological characteristics of the gunpowder before and after the shot as well as to the class characteristics of the analysed cartridges.