General Rifling Characteristics

Shootings frequently occur where no firearm is recovered. The only evidence of the shooting may be a bullet recovered from the scene or the victim. To aid the investigators in searching for the questioned firearm, rifling parameters taken from the recovered bullets can be used to determine the possible manufacturers of the firearm from which the bullets were fired.

General rifling characteristics or GRC are the identified rifling pattern (i.e. 8/right) and the diameters of the individual lands and grooves.  Using these parameters, firearm examiners can search through a database of known rifling data.  The resulting search will help the investigator narrow down the search for the unknown firearm.  

A typical GRC search might involve a 9mm LUGER bullet, fired from a 6/right rifled barrel, with a land width of .055 and a groove width of .125.  Firearm examiners will usually search with a plus or minus .003-.005 tolerance and the results of the search would look something like the data contained in the following table.

Many years ago, a double murder occurred in our community. An elderly couple was found shot to death in their home by their son. It appeared from the scene that there had been a break-in but the son was immediately a suspect. Investigators had a feeling that the son may have committed the crime but could not determine if he had owned or had access to a firearm. Bullets from the scene were examined and it was determined that they were of 38 caliber and were fired from an 8/right rifled barrel. A list of manufacturers was compiled and given to the investigators. Using this list, the investigators searched a weekly "Bargain Mart" classified ad publication. By calling the ads for firearms included on the list of possibilities, the investigators found one individual who said he had sold his revolver to an individual who matched the description of the son. The son was then picked out of a police line-up by the individual who had sold him the gun. When confronted with the evidence the son confessed to the killings.

The database used by firearm examiners all over the world is compiled and maintained by the FBI. The FBI has been recording rifling data from firearms for over 20 years. As new firearms are manufactured, the rifling data is included in the database. Updates to the database are mailed to firearm examiners on an annual basis.  

I have written a General Rifling Characteristics database application for Microsoft's Access that allows you to search against the year 2000 data table.  See the downloads section for more information.

Also, now you can search a limited General Rifling Characteristics file online by clicking here.

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