Chamber marks play an important role in identifying fired cartridges when other marks such as those of the firing pin, breech , etc. are not identifiable . Chamber marks are often imprinted on cartridges fired through locally made firearms. These firearms , commonly known as country- made firearms in India , are manufactured very crudely without proper specifications . The surface irregularities of crudely finished chambers are often highly characteristic and individualize the firearm.
On firing, the cartridge expands and touches the wall of the chamber . The characteristic marks of the chamber are thus imprinted on it. High pressure is normally required for the proper expansion and imprinting of chamber marks. Therefore, at times , a number of rounds has to be fired to obtain proper marks for comparison .But the firing of a number of rounds is avoided as far as practicable, because it usually involves a risk of bursting due to weak joints, weak metal of the barrel, etc. In such cases , it is desirable to adopt an identification procedure which obviates the necessity of firing. If the firearm is not in working order, then it becomes all the more essential to obtain chamber marks without resorting to test firing. The present paper describes a simple and quick method for imprinting chamber marks without test firing.
In a criminal case it was required to identify a 12 -bore fired cartridge case in respect of a suspect country-made pistol chambered for 12 bore cartridges. The pistol was not in proper working order. On examining the cartridge case , it was observed that it had multiple firing pin hits . The percussion was also partially perforated . The firing pin hits were not identifiable. The only identifiable marks present on the questioned cartridge which could permit identification were chamber marks. There were parallel indentations extending from base to mouth of the cartridge (Fig1) . Such marks are often imprinted by crude longitudinal joints inside the chamber. On examining the chamber of the short- barrelled pistol , the corresponding crudely finished joints could be observed even with the naked eye. Imprinting of the joint marks could be tested by firing cartridges , preferably oiled , through the pistol, but it was not possible to fire test cartridges because the pistol was not in proper working order. Thus the chamber marks had to obtained on some other suitable surface , and by means other than firing. In the past, sulphur casts or Wood's metal casts of the chamber have been utilized for the purpose. But instead of preparing a cast of the entire chamber , the relevant portion was taken into consideration. Plasticine was chosen as a suitable material. Being very soft it is capable of imprinting , even under physical pressure applied by hand, the most minute details of the metallic surface irregularities of the portion pressed. Since the relevant location of the joint inside the chamber could be viewed clearly , imprinting of joint marks on plasticine , even by hand pressing , was a simple task. To obtain the replica, plasticine was placed longitudinally over a small flat wooden stick. It was then pressed against the relevant portion of the chamber. The impression of the longitudinal joint with minute surface irregularities was imprinted on the plasticine. The impression could easily be imprinted repeatedly (Fig2). The chamber marks thus obtained on the plasticine could be compared with the chamber marks present on the cartridge case, and the link with the suspected country-made pistol was established (Fig.1&2)
The method adopted was comparatively simple, quick and fool-proof because the minutest details could be imprinted easily; otherwise this cannot be always be ensued, even by firing high pressure rounds. The procedure can be adopted with advantage for marks which can be located precisely inside the chamber and are such that physical hand pressure can be applied uniformly for imprinting the relevant marks. Besides longitudinal joints, small portions bearing characteristic shapes can also be located inside the chamber, and these shapes can be imprinted on plasticine easily provided the relevant mark-bearing portion is not too wide radially (fig3)
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