Letter O

The Definition of Over-Under

Arsenal Exchange - Firearms Classifieds - Industry Directory

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


Button Rifling

Rifling that is formed by pulling a die made with reverse image of the rifling (the 'button') down the pre-drilled bore of a firearm barrel.

Trajectory

The arc described by a projectile (or a load of shot) after it exits the muzzle of a firearm. Falling objects accelerate downwards at a rate of 32 feet per second, per second. The faster a projectile travels, the greater the distance it can cover in a given time before dropping too far. Hence, the higher the velocity of a bullet, the flatter the trajectory it will achieve.

Port

An opening. The ejection port is the opening in the side of a semi-auto from which spent cases are ejected.

Center Hold

A sight picture of when the center of the target is half covered by the front sight when the sights are properly aligned. Also see six o'clock hold and cover hold.

Blown Pattern

A shotgun pattern with erratic shot distribution, generally caused by gas escaping past the wads and getting into the shot.

Riding the Slide

Racking the slide incorrectly by allowing your hand to rest upon the slide as it moves forward during the loading procedure. Riding the slide is a common cause of misfeeds and other malfunctions.

Chain Gun

A type of machine gun or autocannon that uses an external source of power to cycle the firearm.

Gape

The degree to which the barrel(s) of a break-open gun drop down; the size of the opening space, which should be sufficient to allow for ease of loading, unloading and properly-functioning ejection. A good gape is easier to achieve on a side-by-side than an over & under where the bottom barrel is well-enclosed by the action body.

Black Powder

Also known as Gun Powder. A mixture of sulfur, charcoal, and potassium nitrate. It burns rapidly, producing a volume of hot gas made up of carbon dioxide, water, and nitrogen, and a solid residue of potassium sulfide. Because of its burning properties and the amount of heat and gas volume that it generates, gunpowder has been widely used as a propellant in firearms and as a pyrotechnic composition in fireworks. Modern firearms do not use the traditional black powder described here, but instead use smokeless powder.

Hollow-Point Bullet

A type of expanding bullet with a concavity in its nose to increase expansion on penetration of a solid target. Some hollow-point's are also designed to fragment as they expand. They are least likely to over-penetrate the target and harm an innocent bystander. Commonly used for self-defense.

Night Sights

A type of iron sights that glow or shine in the dark, intended for use in low light conditions. Some night sights consist of tiny tubes of tritium, while others use a phosphorus paint.

Crane

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

Airgun (Air Gun)

A variety of pneumatic gun that propels projectiles by means of compressed air or other gas, in contrast to firearms, which use a propellant charge. Both the rifle and pistol forms (air rifle and air pistol) typically propel metallic projectiles, either pellets, or BBs. Certain types of air guns, usually rifles, may also propel arrows.

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.

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.

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.

Underhammer

A type of lock in which the hammer pivots in a vertical arc, striking the nipple on the underside of the barrel. Since the nipple's flash channel goes straight into the powder at the breech end of the barrel, ignition time is very fast. For this reason, and because it gets the hammer out of the way, underhammer locks are commonly used on muzzleloading benchrest rifles which are used for target shooting, and where accuracy is the goal.

Every Day Carry

Term used for a firearm that a person uses as their usual daily carry gun. It is also used to describe a gun that is good for carrying concealed on a regular basis. Factors for determining an EDC may include caliber, physical size, number of rounds, accuracy and/or other factors.

Heavy Trigger

A trigger that requires a lot of pressure to pull it past the break point. Rifles tend to have considerably lighter triggers than handguns, and even a heavy rifle trigger is often lighter than a light handgun trigger.