Letter J Firearms Glossary

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Jacket

A metal, usually copper, wrapped around a lead core to form a bullet.

Jam

A malfunction which locks up the gun so badly that tools are required in order to fix it. Sometimes used to denote a simple malfunction, but many people make a distinction between a complete jam and a simple malfunction.

Jaws

The vise-like device on a flintlock hammer used to hold the flint.

Jeweling

A cosmetic process to enhance the looks of firearm parts, such as the bolt. The look is created with an abrasive brush and compound that roughs the surface of the metal in a circular pattern.

JSP

Abbreviation for jacketed soft point

Jump

The amount of change in the bore axis, measured both vertically and horizontally, while the projectile moves from the chamber to the muzzle when it is fired.


14 Other Firearms Definitions You Need To Know


Headspace Gauge

Plugs of hardened steel, precisely machined in relation to the standard dimensional specifications of a given cartridge, normally in sets of three: "GO", "No-Go" and "Field". By loading these plug-gauges into the chamber in succession, one can check that the action should close on the "Go" gauge. It should not close on the "No-Go" gauge, but might were enough force to be used. And, it absolutely should not close on the "Field" gauge.

Gas Operated

The superheated air created by burning powder. A gas-operated firearm is one that uses the energy from these superheated gases to work the action in semi-automatic and automatic guns.

Shoulder

To bring the butt of a long gun's stock to the shooter's shoulder, preparatory to firing the gun.

Mercury 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't hurt either.

Hang Fire

An unexpected delay between the triggering of a firearm and the ignition of the propellant. This failure was common in firearm actions that relied on open primer pans, due to the poor or inconsistent quality of the powder. Modern weapons are susceptible, particularly if the ammunition has been stored in an environment outside of the design specifications. Reloaded ammunition may also be the cause if not reloaded properly

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.

Jeweling

A cosmetic process to enhance the looks of firearm parts, such as the bolt. The look is created with an abrasive brush and compound that roughs the surface of the metal in a circular pattern.

Creep

Sloppy movement (slack) of a trigger before the actual point of let-off.

Cast Off

An offset of a gun stock to the right, so that the line of sight aligns comfortably with the right eye while the butt of the stock rests comfortably on the right shoulder. Almost all right-handed shooters benefit from a little castoff and most custom built guns are made this way. The only question is how much. The castoff of a gun is about right when, with the gun comfortably mounted, the front bead lines up with the center of the standing breech.
A stock offset to the left, for shooting from the left shoulder is said to be

Sear

The part of the trigger mechanism which holds the hammer or striker back. Pressure on the trigger causes the sear to release the hammer or striker, allowing it to strike the firing pin and discharge the weapon.

Trigger Pull

The entire process of moving the trigger from its forward-most position to its rearward-most position, causing the hammer to fall and the shot to fire.

Safe

A firearm is said to be on safe when its safety is engaged and off safe when it is ready to fire.

Weaver Stance

In the Weaver stance, the body is bladed partly sideways in relation to the target rather than squared towards it (think boxing or martial arts fighter stance). The elbows are flexed and pointed downward. The strong-side arm is slightly straighter than the weak-side arm. Even though the legs are not square to tharget, the hips should be square to the target. The feet should be pointed at the target. The shooter pushes out with the gun hand, while the weak hand pulls back. This produces a push-pull tension which is the chief defining characteristic of the Weaver stance.

Compensator

Also call a Muzzle Brake. A device attached to or made as part of a firearms barrel designed to reduce recoil or muzzle movement on firing. They generally increase muzzle blast.

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