Ballistics - Scientific study of the motion of projectiles; often used as a generic term for the study of bullets from the time they are shot until they impact a target.
Bullet - The projectile that is expelled from a rifled firearm (as opposed to slug).
Cartridge - A complete unfired round of ammunition consisting of a cartridge case, projectile (bullet), primer and smokeless powder.
Cartridge case - The container that holds the cartridge components; usually made of brass, nickel or steel.
Comparison microscope - Two microscopes joined by an optical bridge, which allows the viewing of two samples side by side; it is the primary tool of the firearms examiner.
Firing pin/striker - The working component of a firearm that contacts the ammunition.
Groove - The interior portion of a rifled barrel that is cut to form the rifling; the grooves may vary in number, size and direction of spiral by manufacturer and/or model.
Individual characteristics - Marks present on fired ammunition components that are unique to a particular firearm and distinguish it from all other firearms of the same type; these marks are produced by the random imperfections or irregularities of the firearm surfaces; they are incidental to manufacture and/or caused by use, corrosion, or damage.
Land - The interior portion of a rifled barrel between two grooves
Magazine - A container for cartridges that has a spring and follower to feed those cartridges into the chamber of a firearm; the magazine may be detachable or an integral part of the firearm.
Pistol - A handgun; the most common is a semi-automatic pistol, which uses a magazine and ejects fired cartridge cases automatically.
Primer - The chemical composition that, when struck by a firing pin, ignites the smokeless powder.
Revolver - A handgun that has a rotating cylinder to hold cartridges for firing; cartridge cases are not automatically ejected when fired.
Rifling - Grooves in the interior of a firearm barrel to impart spin to a bullet; improves flight characteristics and increases accuracy.
Shot - Round pellets used as the projectiles in shotshells or cartridges.
Shotgun - A shoulder-fired firearm normally with a smooth barrel.
Shotshell - Shortening of “shotgun shell”; a complete unfired round of ammunition consisting of a shotshell casing, projectile(s) (shot/slug), wadding, primer and smokeless powder.
Shotshell casing - The container that holds the shotshell components; usually made of plastic, with a thin brass base.
Slug - A term applied to a single shotshell projectile.
Striations - 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.
Smokeless powder - The chemical composition that, when ignited by a primer, generates gas; the force of the gas propels the projectile(s).
Striation - The usually microscopic markings on the surface of a fired ammunition component caused by a combination of force and motion; these marks can contain class and/or individual characteristics.
Wadding - Paper or other material in a shotshell that forms a seal between the smokeless powder and the shot.
All glossary terms are from the Association of Firearm and Toolmark Examiners (AFTE) glossary, the Sporting Arms and Ammunition Manufacturers’ Institute (SAAMI) glossary, or are supplied from subject matter experts. A more complete collection of terms is available at the National Institute of Justice Firearms Examiner Training Glossary.