Rim

The edge on the base of a cartridge case which stops the progress of the case into the chamber.

Optical Sight

Usually a telescopic firearm sight.

Pattern

A shotgun term which refers to the manner in which the pellets spread out as they exit the gun. "The pattern" refers to the overall shape of the entire set. A tight pattern is one in which the pellets are closely grouped when they land on target. A loose pattern is one in which the pellets are widely spread.

Hand-Detachable Locks

The firing mechanism of a break-open gun which may be removed for inspection or cleaning without the use of tools. The release latch may be plainly visible or concealed. A feature typically seen on sidelock guns but also on the Westley Richards "droplock" boxlock action.

Cover Hold

Sometimes also known as cover-up hold. A sight picture of when the center of the target is completely covered by the front sight when the sights are properly aligned. Also see center hold and six o'clock hold.

Cartridge

The assembly consisting of a bullet, gunpowder, shell casing, and primer. Cartridges also include shotgun shells and black powder packets used in muzzle loading guns.

Adjustable Trigger

A trigger that can be easily adjusted by the user. Adjustable triggers are common on specialized target-shooting firearms.

Drop-Box Magazine

An extra-deep magazine typical of large calibre rifles for dangerous game. The line of the underside of the wrist does not carry straight forward as with ordinary rifles. Rather the rear of the magazine aligns more towards the center of the forward edge of the triggerguard, typically allowing at least one extra cartridge to be carried.

Bore Diameter

The measurement from one side of the bore to the other. In a rifled barrel this means measurement of the bore before the rifling grooves are cut.

Expanding Bullet

An expanding bullet is a bullet designed to expand on impact, increasing in diameter to limit penetration and/or produce a larger diameter wound. The two typical designs are the hollow point bullet and the soft point bullet. See also Dum-Dum Bullet

Frangible

A bullet that is designed to disintegrate into tiny particles upon impact to minimize their penetration for reasons of range safety, to limit environmental impact, or to limit the danger behind the intended target. Examples are the Glaser Safety Slug and the breaching round.

Colt

A firearms manufacturer started by Samuel Colt in 1855. Colt is most famous for the revolvers they invented and built in the 1800's and the semi-automatic pistol model 1911 designed by John Moses Browning, and for being the first manufacturer of the AR-15 type rifles.

Globe Sight

A front sight assembly, primarily for target rifles, consisting of a tube, housing interchangeable beads and blades. The tube guards against imperfect aiming due to sight pictures influenced by reflections.

Grooves

The cut-away, concave portions of the rifling inside the barrel of a firearm discharging a single projectile.In other words, the lower portion of rifling.

Firing Pin

A needle like metal part of a modern firearm that gives a vigorous strike to the primer initiating the firing of the cartridge.

Cross Dominant

This means a shooter who is right-handed but left-eyed, or left-handed and right-eyed.

Sight Alignment

The manner in which the sights are lined up properly in front of the shooter's eye, to form a straight path to the target.

Long Colt

Although a misused term (even within the firearms industry), Long Colt is a designation for an ammunition cartrige developed by Colt mainly used for revolvers. The actual designation is Colt instead of Long Colt. The term Long Colt was originally coined to avoid confusion between the .45 Colt and .45 ACP cartridges

X-Frame

The frame designation that Smith and Wesson uses for their extra large framed revolvers like the S&W Model 500 and S&W 460XVR

Windage

The setting on the sights used to accommodate the wind or adjust for horizontal (side-to-side) errors in the alignment of the sights with the bore of the firearm.