Porting

Openings at the muzzle end of the gun through which some of the spent gases can escape. Porting reduces perceived recoil and lessens muzzle rise but increases the noise and flash.

Wildcat Cartridge

A wildcat cartridge, or wildcat, is a custom cartridge for which ammunition and/or firearms are not mass-produced. These cartridges are often created in order to optimize a certain performance characteristic (such as the power, size or efficiency) of an existing commercial cartridge. Developing and using wildcat cartridges does not generally serve a purpose in military or law enforcement; it is more a hobby for serious shooting, hunting, gunsmithing and handloading enthusiasts, particularly in the United States. There are potentially endless amounts of different kinds of wildcat cartridges: one source of gunsmithing equipment has a library of over 6,000 different wildcat cartridges for which they produce equipment such as chamber reamers.

Touch Hole

A small orifice at the breech end of the barrel of a muzzle-loading firearm through which the exploding priming charge is conducted from the flash pan to the main charge.

Trapdoor

As in Trapdoor buttplate or Trapdoor Pistol Grip Cap, one of these articles of furniture including a hinged plate, covering a small compartment below in which may be stored several extra cartridges, sight bits, extra springs or pins, cleaning rod, etc.

Trigger Guard

Usually a circular or oval band of metal, horn or plastic that goes around the trigger to provide both protection and safety in shooting circumstances. The shooter's finger should never be within the trigger guard unless the sights are on target and the shooter has made the decision to fire.

Shell Casing

A hollow, piece of metal (or plastic in the case of a shotgun shell) that is closed on one end except for a small hole which holds a primer. The open end holds the bullet. The hollow portion holds the powder. Together the assembled unit is called a cartridge.

Overbore Ammunition

Small caliber bullets being used in large cases. E.g. .22 bullet in a .45 acp case.

Six O'Clock Hold

A sight picture of when the center of the target rests on top of the front sight when the sights are properly aligned. Also see center hold and cover hold.

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.

Comb

The top of a gun's stock, where a shooter rests his cheek when mounting a gun. As it is the top of the stock that determines the position of one's eye, and one's eye is the rear sight on a shotgun, the position of the comb is very important in determining the proper fit of a shotgun.

Disc-Set Strikers

Circular steel fittings, about 1/2 inch in diameter, screwed into the breech face of a gun and through which the firing pins pass. Firing pin bushings allow the convenient replacement of broken firing pins. They also allow the renewal of an older gun where, over the decades, leakage of high-pressure gas from corrosive primers has eroded the breech face around the firing pins; and replacing these bushings with new ones, slightly oversized can compensate for a situation where proper headspace has been compromised.

Ballistic Coefficient

A measure of projectiles ability to overcome air resistance in flight. It is inversely proportional to the deceleration—a high number indicates a low deceleration. Ballistic Coefficient (abbreviated as BC) is a function of mass, diameter, and drag coefficient. In bullets it refers to the amount that drop over distance and wind drift will affect the bullet.

Matchlock

A black powder muzzleloading firearm action which relies upon a serpentine or S-shaped piece of metal to hold a smoldering match. By pressing the lower end of the serpentine, the upper end holding the burning match contacts the priming powder in the pan.

Turn-Bolt Action

A bolt action which is locked by pressing the bolt handle in and down, thereby turning its locking lugs into the receiver.

Red Dot Sight

A type of reflector (reflex) sight for firearms that gives the uses a red light-emitting diode as a reticle to create an aimpoint.

Magazine Well

The opening in the bottom of the gun into which a box magazine is fed. On a semi-auto handgun, the magazine well is at the base of the grip; on a rifle, it is usually placed in front of the trigger guard.

Firing Line

A line, either imaginary or marked, from which people shoot their firearms down range.

Carry

Slang for a gun or the action of carrying a gun concealed, e.g "The Bersa Thunder .380 is a fantastic gun for carrying" or "Do you carry?".

Half Cock

A middle position for an external hammer that effectively provides a safety function. With a firearm with non-rebounding hammers, when on half-cock, the firing pin will not rest on the firing-pin.

Autoloader

A firearm that automatically loads the next cartridge to be fired into the chamber either upon the pull of the trigger in an open bolt design or upon the firing of the previous round in a close bolt design.
Autoloader should not be confused with Automatic or Semi-Automatic since the term Autoloader only applies to how the next round is chambered not how many rounds can be fired per trigger pull. All Automatic and Semi-Automatic firearms are autoloaders. Revolvers, bolt action, lever action and pump action firearms are not autoloaders.