The diameter and weight of a fired bullet may prove helpful in determining the caliber if the bullet is intact and not mutilated. In the absence of correct weight and diameter, examination of class characteristic rifling marks alone can prove helpful. The class characteristic land and groove width, direction of rifling, etc. leads to ascertain the probable calibre. If rifling marks do not pertain to a well-known make and bore, then it may be difficult to determine the calibre unless an exhaustive up to date literature of rifling specifications is available. The problem becomes still more difficult if the questioned bullet is neither intact nor does it carry identifiable characteristic rifling marks and the involved firearm is also not recovered. The present paper describes a case in which the suspect firearm was not available and the bullet recovered from the victim's body was a badly mutilated bullet piece. The bullet piece was a small part of a jacketed bullet, and it did not carry identifiable class characteristic rifling marks. It was required to ascertain the calibre of the firearm, which fired the questioned bullet. The bullet piece was found to be the base portion of a jacketed bullet having a metal jacketed base. The circular metallic base was, however, almost intact. Fig 1.
Fig 1. Bullet piece
In the absence of class characteristic rifling marks , an assessment of type of firearm and its calibre can be made by comparing the diameter of the questioned bullet piece with that of a known calibre bullet, because the calibre of a bullet is usually nominal. Fully jacketed base bullets that are commonly used in this country are .315 /8mm sporting rifle soft nose bullets. Therefore,the bullet piece was compared with the metallic base of a .315 soft nose bullet. For comparison, the base portition of the bullet piece and the base of a standard .315 soft nose bullet were placed on the two stages of a comparison microscope in such a way that the two halves together formed a complete circle. (Fig2)
Bullet piece Test .315 bullet
Fig 2.
The arcs of the circles of two metallic bases were uniformly magnified. The centers of the two circles were determined by geometrical construction. The centers of the two circles were found to be coincident. Thus, the diameters of the two bullets were same which lead to the conclusion that the questioned bullet piece was a part of a .315 bullet and could have been fired through a .315 sporting rifle. It can be seen from the above that in the absence of the suspect firearm, the constructional makeup of the questioned bullet can play an important role in identifying its calibre, even if the bullet is mutilated and class characteristic rifling marks are not identifiable.
