Letter O

The Definition of OTM

Arsenal Exchange - Firearms Classifieds - Industry Directory

19 Other Firearms Definitions You Need To Know


Cartridge Trap

A compartment built into the buttstock of a long gun, usually with a hinged cover, in which are drilled holes deep enough to hold several spare cartridges of the type suitable for use in the specific gun.

Holdopen Toplever

A catch built into the receiver of a break-open gun to keep the toplever in its extreme right position when the barrels are removed. This device makes it slightly easier to remount the barrels. As the barrels are mounted and the breech closed, the barrels contact some kind of release pin (marked with the arrow) and the toplever automatically returns to the center locked position. Because, however, it requires a separate act to find and to depress this tiny tab to re-center the toplever on a broken-down gun, this feature may be irritating when trying to put a gun away in its case.

Naked Bullet

A bullet not covered by a metal jacket or patch.

Derringer

A small single-shot or multi-barreled pocket pistol. Derringers (spelled with two Rs) are called that because of the original desinger and anmufactuturer of that type of gun, Henry Deringer. To get around copyright infringment other designers and manufacturers spell the name with two Rs.

Squib

An underpowered powder charge, usually caused by a fault in cartridge loading, often insufficient to expel a projectile from the muzzle of a firearm. If such a blockage is not cleared, the next attempted shot could cause the barrel at least to bulge, and very possibly to burst.

Recoil Crossbolt

A steel bolt, mounted transversely through a rifle stock just under and behind the front (and sometimes rear) receiver ring, sometimes concealed in the wood and usually against which the action is carefully bedded. When properly fitted, it helps distribute the recoil and reinforces stock at the point where wood has been removed to accept the action. Recoil crossbolts can be recognized by the flush-mounted circular steel fittings on the side of the stock, but are sometimes finished with contrasting wooden plugs and sometimes concealed completely. Also called Reinforcing Crossbolt.

Cartridge Overall Length

This is the maximum overall length the cartridge can be (and is expected to be) in order to function properly in magazines and the mag well of a bolt action rifle.

Caliber

The diameter of the bore of a firearm measured as a fraction of an inch. Although such a measurement may be frequently stated in millimeters. It is correctly expressed as ".40 caliber" (note the decimal point) or as "10 millimeter" (without "caliber" or the leading decimal point). Caliber numbers when used to identify the size of the bullet a gun will file are usually followed by words or letters to create the complete name of the cartridge. These letters often represent a brand name or an abbreviation for the name of the company that first introduced the round.

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.

Failure To Feed

A semi-automatic firearm malfunction in which the slide passes entirely over the fresh round, failing to pick it up to insert into the chamber as the slide returns to battery.

Doll's Head

A rib extension on a break-open gun, ending in a circular or semi-circular shape in plan (resembling the head of a doll), mating into a similarly-shaped recess in the top of the receiver, designed to resist the tendency of the barrels to pull away from the standing breech when firing. Because an action's centerpoint of flexing when firing is at the base of the standing breech, not at the hingepin, a passive doll's head extension makes an effective extra fastener, even without additional mechanical locks operated by the opening lever.

Handgun

Synonymous with pistol. A small, short-barreled firearm designed to be fired while held in one or both hands, possibly small enough to be concealed on the person, rather than while braced against the shoulder. The term includes antique dueling pistols, modern single-shot, semi-automatic pistols and revolvers.

Bandolier

A pocketed belt for holding ammunition and cartridges. It was usually slung over the chest. Bandoliers are now rare because most military arms use magazines which are not well-suited to being stored in such a manner. They are, however, still commonly used with shotguns, as individual 12 gauge shells can easily be stored in traditionally designed bandoliers.

Scope Blocks

A pair of small dovetailed steel bases, screwed usually one to the barrel and one to the front receiver ring of a rifle, to accept mounts for target scopes such as the Unertl where the scope is allowed to move forward in the rings under the recoil of the rifle and which typically carry the windage and elevation adjustments in the mount.

Carbine

A rifle with a relatively short barrel.

Pump Action

A type of mechanism for removing a spent shell casing from the chamber of a firearm and inserting a fresh cartridge into the chamber. This type of mechanism is most commonly used in shotguns and rimfire rifles.

Cylindro Conoidal Bullet

A hollow base bullet, shaped so that, when fired, the bullet will expand and seal the bore. It was invented by Captain John Norton of the British 34th Regiment in 1832, after he examined the blow pipe arrows used by the natives in India and found that their base was formed of elastic locus pith, which by its expansion against the inner surface of the blow pipe prevented the escape of air past it.

Saddle Ring

A steel ring, around an inch in diameter, mounted to a stud, usually on the left side of the receiver of a carbine, to which may be tied a leather thong to secure it to a saddle or a scabbard so as not to lose the carbine when riding a rambunctious horse.

Knurled Surface

A metal surface which contains a pattern of ridges or beads.