Glossary of Firearms Terms - I

I

• improved cartridge: A wildcat cartridge that is created by straightening out the sides of an existing case and making a sharper shoulder to maximize powder space. Frequently the neck length and shoulder position are altered as well. The caliber is NOT changed in the process.

• IMR powder or Improved Military Rifle: A series of tubular nitrocellulose smokeless powders evolved from World War I through World War II for loading military and commercial ammunition and sold to private citizens for reloading rifle ammunition for hunting and target shooting.

• improvised firearm: a firearm manufactured by someone who is not a regular maker of firearms.

• internal ballistics: A subfield of ballistics, that is the study of a projectile's behavior from the time its propellant's igniter is initiated until it exits the gun barrel. The study of internal ballistics is important to designers and users of firearms of all types, from small-bore Olympic rifles and pistols, to high-tech artillery.

• iron sights are a system of aligned markers used to assist in the aiming of a device such as a firearm, crossbow, or telescope, and exclude the use of optics as in a scope. Iron sights are typically composed of two component sights, formed by metal blades: a rear sight mounted perpendicular to the line of sight and consisting of some form of notch (open sight) or aperture (closed sight); and a front sight that is a post, bead, or ring.