Each bullet or shell casing has two distinct properties when it comes to firearm identification. The design of a barrel’s rifling, such as four grooves with a right twist, the width of lands and grooves, and its caliber are all class features. Class characteristics are a subset of individual characteristics. These are “distinctive, unique marks developed during the manufacturing process, such as the impression left by a deformed or broken firing pin or the odd striations left on a bullet by a spur on a sawn barrel,” according to Schehl. These features allow examiners to compare and classify things in evidence, resulting to one of three outcomes.
1.) When the expert discovers a match between two ammunition components or a match between an ammunition component and a firearm, this is referred to as a “identification” finding.
2.) An “exclusion,” on the other hand, indicates that there is no match between the objects being examined.
3.) Finally, “no conclusion” signifies that the bullet or casing could not be definitively recognised or ruled out as having been fired from a specific firearm.
While the class features of a specific piece of evidence may correspond with a known sample—for example, the examiner can conclusively conclude the cartridge originated from a.44 calibre handgun—there is insufficient evidence to correlate the evidence’s individual characteristics to a specific pistol. Identifying class features on a certain piece of evidence will help law enforcement officers with their investigations.
The class characteristics eliminate a large range of weapons from consideration and may assist detectives in focusing on certain individuals who have previously been associated with the sort of weapon in question. However, given the enormous number of separate parts that make up a specific make and model of a handgun, this can be a daunting undertaking. That is why determining individual traits is so important, and modern computer technology makes this element of the examiner’s job a little easier.