Letter U

The Definition of Underlug

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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.


19 Other Firearms Definitions You Need To Know


Primer Ring

Refers to a visible dark ring created by the primers in centerfire ammunition around the firing pin hole in the frame after much use.

Follower

A smooth, sometimes contoured plate, within a magazine, at the top of a spring, across which cartridges slide when being loaded into a chamber.

Back Bored

A shotgun barrel that has a bore diameter increased beyond standard specifications, but less than the SAAMI maximum. Done in an attempt to reduce felt recoil, improve patterning, or change the balance of the shotgun.

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.

Reticle

A matrix of dots, posts or lines, visible inside a rifle's telescopic sight, normally adjustable via exterior knobs for windage and elevation. After careful adjustment at a known range, the shooter aims the rifle by superimposing this matrix onto the target. With good estimation or range, cooperation from the wind, a clear eye and a steady hand, he may have a reasonable expectation of hitting his target.

Frangible

A bullet that is designed to disintegrate into tiny particles upon impact to minimize their penetration for reasons of range safety, to limit environmental impact, or to limit the danger behind the intended target. Examples are the Glaser Safety Slug and the breaching round.

Necking Down

Shrinking the neck of an existing cartridge to make it use a bullet of a different caliber. A typical process used in the creation of wildcat cartridges.

Stopping Power

A popular but imprecise term used to refer to the ability of a small arms cartridge to cause a human assailant or an animal to be immediately incapacitated when shot with it. A more precise term is be Wound Trauma Incapacitation (WTI).

Striker

In a handgun that does not have a hammer, the striker is a linear driven, spring loaded cylindrical part which strikes the primer of a chambered cartridge. The striker replaces both the hammer and firing pin found in hammer driven pistols.

Capper

A hand tool used in the field for inserting live and removing spent primers from cartridges.

Parallax

This occurs in telescopic sights when the primary image of the objective lens does not coincide with the reticle.Telescopic sights often have parallax adjustments to minimize this effect.

AD

Abbreviation for Accidental Discharge

Fulminate Of Mercury

A highly sensitive explosive used as a primer compound.

Dum-Dum

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. Expanding bullets were given the name Dum-dum, or dumdum, after an early British example produced in the Dum Dum Arsenal, near Calcutta, India by Captain Neville Bertie-Clay in the the mid-1870s. Modern sef-defensive, JHP (Jacketed Hollow Point), ammunition are based on the original dum-dum ammunition design and principles.

Powder Charge

The amount of propellant powder that is suitable for specific cartridge-bullet combination, or in the case of shotshells, for a specific weight of shot and wad column.

Cylinder

The part of a revolver that holds cartridges in separate chambers radially around a central hingepin. The cylinder revolves as the handgun is cocked, , either to the left or to the right depending on the gun maker's design, bringing each successive cartridge into position, and locked into alignment with the barrel for firing.

Line Of Sight

An imaginary straight line from the eye through the sights of a firearm to the target.

Drop Safety

A mechanical safety that prevents a gun from firing when it is unintentionally dropped.

FPS

Abbreviation for feet per second. A term used in expressing the velocity of a bullet.

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