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


Ballistics

The science of cartridge discharge and the bullet's flight. Internal ballistics deals with what happens inside of a firearm upon discharge. External ballistics is the study of a projectile's flight, and terminal ballistics is the study of the impact of a projectile.

Fouling

The accumulation of unwanted material on solid surfaces. The fouling material can consist of either powder, lubrication residue, or bullet material such as lead or copper.

Muffs

Slang for Ear Muffs.

Ballistic Coefficient

A measure of projectiles ability to overcome air resistance in flight. It is inversely proportional to the deceleration—a high number indicates a low deceleration. Ballistic Coefficient (abbreviated as BC) is a function of mass, diameter, and drag coefficient. In bullets it refers to the amount that drop over distance and wind drift will affect the bullet.

Floor Plate

The detachable plate at the bottom of the cartridge magazine.

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"

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.

Muzzle Control

Being aware of and responsible of which direction your firearm is pointed at all times, and always keeping it pointed in a safe direction.

Casehardening

A heat-treating process that incorporates carbon into the surface molecular structure of the steel, providing a hard-wearing surface without making the entire receiver brittle. The parts to be casehardened are packed in a crucible with carbon-rich media such as bone meal and charcoal, heated to bright orange, about 1800°F, then quenched in bubbling oil. Also called Carbonizing.

CQC

Abbreviation for Close Quarters Combat.

Lever Action

A type of firearm action which uses a lever located around the trigger guard area, (often including the trigger guard itself) to load fresh cartridges into the chamber of the barrel when the lever is worked.

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

Doughnut Pattern

A shotgun pattern with a hole in the middle generally caused by the interference of the top wad.

NFA

National Firearms Act of 1934. Enacted on June 26, 1934, currently codified as amended as I.R.C. ch. 53, is an Act of Congress in the United States that, in general, imposes a statutory excise tax on the manufacture and transfer of certain firearms and mandates the registration of those firearms. The Act was passed shortly after the repeal of Prohibition. The NFA is also referred to as Title II of the Federal firearms laws.
The NFA includes:

  • Requires the registration of all fully automatic firearms.
  • Requires the registration of all "sawed off" rifles and shotguns.
  • Requires the registration of firearm silencers.
  • Imposes a $200 transfer tax on the above items.

Rail

A feature on some guns which allows various aftermarket accessories to be attached the firearm such as flashlights or lasers. On pistols, if equipped, the rail is on the underside of the frame below the barrel. On rifles, a rain can be found above or below the barrel, with AR type rifles, the forestock can be made of rails allowing all kinds of attachments in various positions.

Toe

The bottom of the butt-end of a gun stock.

CCP

Abbreviation for Concealed Carry Permit.

BUG

Abbreviation for 'Back Up Gun'

Ambi

Short for the word Ambidextrous. Meaning that a feature of a firearms can be used by either hand, for example ambi-safety, ambi slide catch or ambi mag release.