Bullet identification by non-striated land and groove marks
of abnormally undersized barrels
 
J K Sinha et al.

[ Forensic Science International, 4(1974)43-45, Netherlands(Elsevier)]


 
           Summary
  Investigations of bullets fired through abnormally undersized rifled barrels and examined on the basis of class and individual characteristic marks have been discussed. Whereas the identity of such bullets in most cases can be established from non-striated land and groove marks by naked eye examination, their elimination on the basis of class characteristics may at times be misleading.


  Identification of fired bullets by class and individual characteristic rifling marks is well known.But bullets fired through abnormally undersized riled barrels usually carry different rifling marks. In this paper characteristic marks on bullets fired through such barrels have been investigated with special reference to imitation revolvers. Imitation of .32 revolvers are often used in crimes in this part of our country. Although they do not conform to standard specifications, their barrels are rifled. Their bore diameter is abnormally less and they may be as small as .29 inch. A regular .32 inch fired through such a barrel is likely to become elongated while passing through such an abnormally small diameter bore. Jacketed bullets, being comparatively harder, may not elongate, and may get lodged inside the weapon. Although the chamber of imitation revolvers can accommodate with ease both .32 revolver and auto cartridges with lead and jacketed bullets , it is risky to fire jacketed bullets through such barrels as impaction of the bullet may cause barrel to burst.

The process of elongation and the high-velocity of the forward motion of the bullet tend to deflect it from the path and direction of the rifling , and consequently such bullets may not engage the rifling properly. Moreover, the bullet is also shaved during the process of elongation and shaving is likely to imprint mixed land and groove marks without any clear demarcation. For these reasons it may be difficult the number of lands and grooves of the firearm from which the bullet was fired. Comparison of such fired bullets on the basis of class characteristics without firing test bullets through the same firearm may lead to erroneous results.

Jacketed bullets passing through such barrels will engage the rifling initially and will move in the direction and path of the rifling until arrested due to oversize and their inability to elongate. Such bullets are identifiable without any test firing as far as the class characteristics are concerned. Characteristic class marks on jacketed bullets can not be compared with the marks on unjacketed bullets fired through such barrels.

Comparison of individual characteristic marks on bullets fired through undersized rifled barrels is comparatively easier and more reliable. Because the bullets do not travel along the predetermined path from breech to muzzle end, characteristic breaks in the rifling marks are usually observed. Surface irregularities or notches, if any, on the lands and grooves are also prominently imprinted on the bullet. The characteristic break, shape, size, relative position of rifling marks and shaving can be used to identify the fired bullet in respect of the firearm. The importance of these characteristic marks is clear, especially when the bullets are mutilated and characteristic striations of land and groove marks are not sufficient to permit identification. Although the marks are so pronounced and characteristic that positive identification in some cases is possible even by naked-eye examination and comparison, it is preferable to carry out a comparison at a low- power magnification before arriving at any conclusion.( FIG 1)

Jacketed bullets lodged inside a weapon usually cannot be identified in respect of the firearm as far as the individual characteristic marks are concerned. Due to their arrest the bullets do not carry striations from breech to muzzle end. The striations present cannot be compared with the striations on the elongated lead bullets fired through the same barrel because the path traversed by elongated lead bullets may be different and the marks may be overlapped due to deflection of the bullet during the process of elongation and forward propulsion. In the absence of any suspect firearm comparison of elongated lead bullets with metal jacketed bullets is likely to mislead the investigator. Therefore one should be cautious in comparing an abnormally elongated lead bullet with a metal jacketed bullet.

non strited rifling marks
FIG.1
Characteristic non-striated land and groove marks
on bullets fired from abnormally undersized rifled barrel.


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