**New calibre/bore designation for mismatched rifled
and non standard smooth bore firearms.

J. K. Sinha.

Identification of projectiles fired from smoothbore, improvised
and home made firearms-- Author's Ph.D.thesis


**Part of a chapter of thesis--    Brief description**
 
Non standard firearm's nomenclature
      Non standard firearms(home built,imrpovised or imitation)are manufactured/made without adhering to proper specifications, quality control and legal requirements imposed by the Government. Their constructional features are so different from the standard legal firearms that they defy normal nomenclatures. Unlike standard firearms,the bore/calibre of non standard firearms can not be designated by their internal bore dimensions because they may not necessarily correspond to the specified bore dimensions of corresponding standard rifled /smooth bore firearms. However, they may conveniently be designated by the calibre/ bore of the ammunition they are designed to load and fire irrespective of their bore dimensions(more or less).But designation by the type of the ammunition alone may be deceptive as barrel marks and ballistics may vary significantly even amongst similarly designated firearms using similar or different ammunition because

       a) they may not necessarily have the same bore dimensions and may vary widely
         from one firearm to the other
      b) the same firearm may load and fire different calibre ammunition   .
   
    .45, 303,.315 fired from
    same home made pistol
       c) the bore may vary appreciably from breech to the muzzle.

    It is thus apparent that in addition to the type of ammunition, bore dimension is also an important parameter for a meaningful evaluation of forensic problems in cases involving non standard firearms. But it is impractical to measure and designate variable bore dimensions from breech to muzzle. Instead of making absolute measurements ,relative projectile-bore diameter i.e., relative bullet-bore diameter for rifled cartridges and relative wad-bore diameter for shotgun cartridges,can conveniently be measured/assessed. The sub classification on the basis of bullet -bore diameter or wad-bore diameter is practical, convenient and very useful in evaluating problems of forensic interest.
  Relative bullet-bore diameter designation:
    Assessment of relative bullet-bore diameter of a non standard made firearm can conveniently be made by dropping an unfired/fired bullet from both breech and muzzle ends of the barrel.
  •   If the bullet passes through the bore without obstruction, then the firearm is designated as oversize bore firearm
  •   If the bullet on dropping from breech or muzzle gets stuck near the chamber and muzzle  except for the ogival portion, then the firearm is designated as undersize bore firearm
  •   If the bullet moves freely inside the bore only up to a certain distance when dropped either from breech or muzzle or from both ends and gets stuck inside the barrel, then the bore is said to be variable i.e., oversize as well as under-size, and the firearm is designated as variable or mixed size bore firearm.
  Thus, a .303 oversize home made pistol refers to a short barreled locally made firearm designed to fire .303 rifle cartridges having its bore diameter more than the diameter of a .303 bullet whether uniform or otherwise.

Relative wad-bore diameter designation.
   An unfired wad meant for sealing the bore  is dropped to assess the relative bore size of  firearms designed for firing shotgun cartridges. The firearm is classified accordingly as undersize, oversize or mixed size bore firearms.

Mismatched ammunition  fired from rifled /smooth bore firearms
                     Some firearms (rifled/smoothbore) can easily load and fire mismatched cartridges. They behave like non standard firearms when a mismatched cartridge is fired. The mismatched bullet may remain undersized or over sized inside the rifled bore. The relative bullet-bore diameter markedly influence barrel marks(class and individual characteristics) , wounding effect (entrance and exit holes), range and angle of fire, casualty criteria etc.  Therefore, for a meaningful explanation and proper evaluation of forensic problems , it is warranted that the involved firearm may be designated as undersized or oversized in relation to the designated nominal bore diameter. Thus, a .30-06 rifle firing mismatched .270 winchester cartridges may be referred as a non standard .270 over sized rifle for the purpose of barrel marks and trajectory evaluation. Besides under/over size, some times the bullet diameter of mismatched ammunition(on setup or otherwise) corresponds to appropriate ammunition. Such a bullet may engrave proper rifling of the mismatched firearm. Thus, they may be designated by both the bullet and the firearm. (.303 bullet fired from .32-40 rifle).

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Consultation/Enquiry:--Mail to Author


** Theory, experimental details and illustrative photographs in author's forthcoming book titled
       " Unusual forensic ballistics and shooting reconstruction"


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