Letter U

The Definition of Underlug

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Underlug

The locking lugs on a break-action firearm that extend from the bottom of the barrels under the chamber(s) and connect into the receiver bottom.


19 Other Firearms Definitions You Need To Know


Percussion Cap

A small metal explosive-filled cup which is placed over the nipple of a percussion firearm. As the cap is struck by the hammer, it explodes and sends a flame through the flashhole in the nipple to the main powder charge.

Capper

A hand tool used in the field for inserting live and removing spent primers from cartridges.

Sling

A long strip of leather, plastic, or nylon which is fastened at the fore and rear of the gun for the easy carry of long guns.

Double-Barreled Shotgun

A shotgun with two barrels, usually of the same gauge or bore. The two types of double-barreled shotguns are over/under (abbreviated as O/U or OU), in which the two barrels are stacked on top of each other, and side-by-side (abbreviated as SxS), in which the two barrels sit beside each other. See photo at right for example of side-by-side double-barreled shotgun. For double-barreled guns that use one shotgun barrel and one rifle barrel, see combination gun.

Railgun

A railgun is an electrically powered electromagnetic projectile launcher based on similar principles to the homopolar motor.
Using a magnetic field powered by electricity, a rail gun can accelerate a projectile up to 52,493 feet (16,000 meters) per second.
A railgun consists of two parallel metal rails (hence the name) connected to an electrical power supply. When a conductive projectile is inserted between the rails (at the end connected to the power supply), it completes the circuit. Electrons flow from the negative terminal of the power supply up the negative rail, across the projectile, and down the positive rail, back to the power supply.

Decocker (De-Cocker)

On semi-auto matic pistols, a lever that mechanically lowers the hammer without firing the gun.

Point of Impact

The point where the projectile from a firearm hits.

Sporting Firearm

Any gun that can be used in a sport.

Feed

The action of moving live cartridges from the magazine of a firearm into the chamber.

Grip Safety

A passive, external safety typically located on the backstrap, which must be fully depressed to release the trigger. Most 1911-pattern pistols feature a grip safety.

Flintlock

A system of firearms ignition, in general use circa 1660 - 1825, whereby the pull of a trigger releases a sear from a notch in a spring-loaded hammer, which holding a properly knapped piece of flint, strikes a vertical slab of steel (called a frizzen) scraping off tiny molten particles of the steel, and pushing it forward causes an integral flashpan cover to open forward, exposing a bit of fine gunpowder below, which when contacted by the falling sparks, ignites and sends a flash of fire through the touchhole, into the loaded breech setting off the main charge and firing the gun. The Flintlock system was supplanted by the Percussion system around 1820.

Corto

Italian for "short." Seen as part of a cartridge designation. On some Italian manufactured guns that use .380 ACP, the designated caliber is 9mm Corto (9mm Short), which is also the same as the German 9mm Kurtz

Needle Gun

A needle gun is a bolt-action firearm (the first known type of bolt action rifle) that has a needle-like firing pin, which can pass through fully self-contained (paper) cartridge case to strike a percussion cap at the bullet base. The first experimental needle gun was designed by Jean Samuel Pauly, a Swiss gunsmith, in 1812. The first mass-produced needle gun was invented by the German gunsmith Johann Nicolaus von Dreyse, who, beginning in 1824, had conducted multiple experiments, and in 1836 produced the first viable breech loading gun model using a complete cartridge .

Naked Bullet

A bullet not covered by a metal jacket or patch.

FOPA

Firearm Owners' Protection Act of 1986. It is a United States federal law that revised many provisions of the Gun Control Act of 1968. It bans civilian ownership of machine guns manufactured after May 19, 1986. Firearms made and registered before that date are not affected. The law limits the Bureau of Alcohol, Tobacco and Firearms from inspecting gun dealers more than once a year, with follow-up inspections allowed only The law also specifically forbids the government from creating a national registry of gun ownership.

Primer

A small metal cup that contains a tiny explosive charge that is sensitive to impact. A primer is placed in the base of a shell casing to ignite the powder of the completed cartridge. It is detonated by the striking of a firing pin in the firearm.

Over Travel

If the trigger is able to continue moving to the rear after the shot has fired, the trigger is said to over-travel.

Short Trigger

A trigger that doesn't have to travel very far before it reaches the break. In a 1911 semi-auto pistol, a short trigger is a different part than a long trigger, and (in addition to providing less motion) it features a shorter reach which may be of benefit to a small-handed shooter.

Bore Axis

An imaginary line which runs right down the center of the handgun's barrel and out though the back end of the gun. A handgun may have a high bore axis, with the imaginary line running out into space well above the shooter's hand. Or it may have a low bore axis, with the imaginary line running either straight through the shooter's hand or just skimming the surface slightly above her hand. A high bore axis tends to create greater perceived recoil and more muzzle flip when firing the gun than does a low bore axis.