Letter O

The Definition of Over-Under

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Over-Under

Can also be spelled Over/Under, OverUnder or Over and Under. A firearm (most commonly a shotgun) with two barrels that are vertically aligned with each other, one on top of the other.


19 Other Firearms Definitions You Need To Know


Action

The working mechanism of a firearm involved with presenting the cartridge for firing, and in removing the spent casing and introducing a fresh cartridge. For example some of the most common types of Actions are single, double, bolt, lever and pump.

Neck

The forward portion of a bottlenecked cartridge case. Also the portion of a rifle chamber in which the neck of the cartridge case rests.

Co-Witness Sighting

Co-Witness Sighting is the use of any iron sight mounted onto a rifle that is fitted with an optical sight as a primary sighting system. They come in two basic configurations, fixed or flip-up. The idea is that if you align your red dot and your iron sights you have a backup aiming system on the gun.

Double Action

An action type that when the trigger of a gun is pulled, the gun gets cocked and the hammer (or striker) is dropped. This applies to both revolvers and semi-automatic guns. On a double action revolver, when the trigger is pulled, the hammer is cocked before releasing. With a double-action semi-automatic pistol, the hammer does not have to be manually cocked (via actually pulling back the trigger or tracking the slide), the hammer (or striker) will be cocked while the trigger is being pulled. A firearm that only the hammer drops when the trigger is pulled is a single action gun.

Pepperbox

An early form of muzzle-loading revolver wherein, instead of the current practice of having one barrel mated to a multi-chambered rotating cylinder, multiple joined barrels revolve together around a central axis.

Thunder

With the execption of the BP model series, Thunder is the name of all of Bersa's pistols. The line currently consists of three frames.

• The Thunder .380 series, which is a very reliable and good looking compact blowback system .380 acp pistol (there is also a .22lr version).
• The full size Thunder Pro series (avalable in 9mm and .40 S&W) is a locked breech design.
• The Thunder Ultra Compact Pro series, locked breech, short recoil design which is more of a commander size Thunder Pro (available in 9mm, .40 S&W, and .45 acp).
The Bersa Thunders are well known among firearms enthusiasts for being extremely high quality guns at reasonable prices.

Obturation

The process of a bullet expanding under pressure to fit the bore of the firearm, or a cartridge case expanding under pressure to seal the chamber.

Powder

The chemical propellant which is burned to produce the hot gases which send the projectile flying downrange.

Pan

The small dished container located on the side or top of a matchlock, wheel-lock or flintlock forearm used to hold the priming powder charge.

Sabot

An oversized, lightweight housing that allows a sub-calibre projectile to be fired in a larger-diameter bore, usually in the interest of increased velocity. The sabot falls away from the actual projectile upon exiting the muzzle. For example, a hunter could use his .30-30 deer rifle to shoot small game with .22 centerfire bullets.

Range Finder

A device used to determine the range to a target. Many range finders work by bouncing a laser beam off the target or nearby object and measuring the time for the reflection to arrive back at the instrument. It is also possible to use various passive optical devices such as a mil-dot telescopic sight.

HMR

Abbreviation for Hornady Magnum Rimfire.

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?".

Bayonet Lug

A mounting point on a small arm that allows a bayonet or other accessory to be attached.

Slamfire

A premature, unintended discharge of a firearm that occurs as a round is being loaded into the chamber.

Throat

The beginning of the bore of a rifled firearm. The transition between the chamber and the rifling. The area most vulnerable to erosion from high velocity cartridges.

Drum Magazine

A type of firearms magazine that is cylindrical in shape, similar to a drum. Probably the most recognizable drum magazine is the magazine for a Thompson carbine rifle, also known as the Tommy Gun.

Crane

A swing-out arm on a revolver, to which the cylinder is mounted when opened facilitates loading and cleaning.

Holographic Weapon Sight

a non-magnifying gun sight that allows the user to look through a glass optical window and see a cross hair reticle image superimposed at a distance on the field of view. The hologram of the reticle is built into the window and is illuminated by a laser diode.

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