Letter U

The Definition of Underbolts

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Underbolts

A sliding bar, running longitudinally through the watertable of a break-open side-by-side gun's action, with openings through which the lumps of the barrels pass when the gun is closed. Under spring tension, this bar moves forward when the opening control is released and its two locking surfaces engage complementary slots (bites) in the rear of the two barrel lumps. Originally operated by a hinged tab in front of the trigger guard. Now invariably operated by a cam from Scott's [toplever] spindle. Most modern side-by-side guns lock closed in this manner.


19 Other Firearms Definitions You Need To Know


Chamber Throat

This is the area in the barrel that is directly forward of the chamber, which tapers to the bore diameter.

Mag

Slang word for Magazine.

Integral Lock

A built in lock that may prevent the firearm from being fired.

Negligent Discharge

The unplanned discharge of a firearm caused by a failure to observe the basic safety rules, not a mechanical failure of the gun.

Anson & Deeley Action

A type of internal hammer side by side shotgun boxlock action. It was patented in 1875 and is the essence of simplicity utilizing only two springs and three moving parts (per barrel). One of the most successful action designs ever, and still produced to this day by most SxS shotgun manufacturers.

Matched Pair

Two firearms that are manufactured identical in every way and are sequentially serial numbered and are sold as a set. The most common type of matched pair guns are cowboy style revolvers for a couple of reasons, both guns will feel exactly the same in the hands and they make the set more collectable.

Ear Muffs

Hearing protection that completely covers both ears and is usually attached to a headband.

Recoil Compensator

A device fitted inside the buttstock of a heavily-recoiling gun or rifle, usually containing mercury and a valve. As the gun recoils, the mercury is displaced temporarily, increasing the duration, and thus diminishing the perceived impact of the recoil. The added half-pound of weight doesn#39;t hurt either.

Pinfire

An early form of complete, self-contained cartridge. It included bullet, powder and ignition primer, all in one package. The primer was located towards the base of the cartridge, but completely internally. The pin, shaped like a little finishing nail, pointed on the inside end and resting on the internal primer, projected radially about a quarter-inch to the outside of the base of the cartridge. When loaded, a pinfire gun showed the tips of the pins exposed through small slots in the tops of the breech faces of the barrels. To fire, hammers fell on the pins, driving them (through the wall of the cartridge) into the internal primer.

Failure To Extract

A semi-automatic firearm malfunction in which the extractor fails to move the empty case out of the way as the slide travels back. A failure to extract often causes double-feed malfunction.

Expanding Bullet

An expanding bullet is a bullet designed to expand on impact, increasing in diameter to limit penetration and/or produce a larger diameter wound. The two typical designs are the hollow point bullet and the soft point bullet. See also Dum-Dum Bullet

Birdshot

A type of shotgun ammunition which uses very small pellets with individual projectiles of less than .24" in diameter designed to be discharged in quantity from the shotgun. The size of the shot is given as a number or letter-- with the larger number the smaller the shot size. It is so named because it is most often used for hunting birds. The finest size generally used is #9 which is approximately .08" in diameter and the largest common size is #2 which is approximately .15"

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.

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.

Point Blank Range

The farthest distance that a target of a given size can be hit without holding over or under with the sights. The exact range is determined by the performance of the cartridge used, the ZERO range, and the accepted size of the target area. This term is not to be confused with point blank shooting.

LCI

Abbreviation for Loaded Chamber Indicator

Malfunction

A misfeed or other failure to fire which can be cleared on the spot and without tools.

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.

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.

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