Identification Process

A tool is the harder of two objects, which when brought into contact with each other, results in the softer one being marked. This marking is known as a toolmark.

Firearms identification is simply a firearms-related specialized subset of the broader field of toolmark identification.

When the various parts of the mechanism of a firearm come into hard contact with a cartridge case or shotshell case (typically made of a relatively softer metal such as brass), a toolmark can be created.

The cycle of fire includes a number of steps that are common to all firearms:

• Feeding of a cartridge manually or from a magazine
• Chambering of a cartridge
• Locking of the breech or bolt mechanism
• Firing by releasing of the firing pin
• Obturation, specifically, sealing of powder gases forward of the cartridge case or shotshell case by expansion of the cartridge case to fully fill the chamber, as well as by expansion of projectiles or wadding material
• Unlocking of the breech or bolt mechanism
• Extraction of the fired cartridge/shotshell case
• Ejection of the fired cartridge/shotshell case
• Cocking of the firing mechanism

These steps may be performed manually, semiautomatically, or fully automatically. Depending on the design of a firearm, certain steps may be combined.

Striated marks occur when there is relative motion between two objects under pressure. Striations are contour variations (generally microscopic) on the surface of an object caused by a combination of force and motion, where the motion is approximately parallel to the plane being marked. Striated toolmarks could also be described as scratch marks, abrasion marks, or friction marks.

Impressed toolmarks (compression marks) occur when a tool is placed against another object and sufficient force is applied to the tool that an impression is made. The class characteristics (size and shape) can indicate the type of tool used to produce the mark. These impressions can also contain individual characteristics of the tool producing the mark.

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