Class and Individual Characteristics of Bullets

When a bullet is fired down a rifled barrel, the rifling imparts a number of markings to the bullet that are called "class characteristics." These markings may indicate the make and model of the gun from which the bullet has been fired. They result from the specifications of the rifling, as laid down by the individual manufacturer. These characteristics are:

1. Number of lands and grooves

2. Diameter of lands and grooves

3. Width of lands and grooves

4. Depth of grooves

5. Direction of rifling twist

6. Degree of twist

In addition to these class characteristics, imperfections on the surfaces of the lands and grooves score the bullets, producing individual characteristics. For lead bullets these individual characteristics are more pronounced where the grooves score the bullet. In contrast, for jacketed bullets, the land markings are the most pronounced.1 These individual characteristics are peculiar to the particular firearm that fired the bullet and not to any others. They are as individual as fingerprints. No two barrels, even those made consecutively by the same tools, will produce the same markings on a bullet. Thus, while the class characteristics may be identical on bullets fired by two different weapons, the individual characteristics will be different. In addition to markings on the bullets, the magazine, firing pin, extractor, ejector, and breech face of a weapon may all impart class and individual markings to a cartridge case or primer.

0 0

Post a comment