Letter M

The Definition of Machine Gun

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Machine Gun

A fully automatic firearm that rapidly fires multiple rifle-caliber shots with a single pull of the trigger.


19 Other Firearms Definitions You Need To Know


Plus P

Also spelled "+P" or "P+". Is small arms ammunition that has been loaded to a higher internal pressure than standard for it's caliber. Many calibers are available in both standard and +p or +p+ variants. Ammunition marked +p produces more power and higher pressures than the standard ammunition. Not all firearms are designed to handle the increased pressure consult your owner's manual or gun manufacturer before using +P ammunition.

Drop Safety

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

LR

Abbreviation for Long Rifle. Typically used in the .22 caliber cartridge designation .22LR. However can be used as an abbreviation for Kentucky Long Rifle

Eye Dominance

Although we have two eyes for depth perception and for spare parts, there is a natural tendency for one eye (the master eye) to take precedence over the other, regardless of the relative visual acuity of each eye. It is a fortunate condition when the eye on the side of the shoulder where one is comfortable mounting a gun is also the dominant eye.
To test for eye dominance:

Pick out a small object several feet away. With both eyes open, center your right index finger vertically over the object. Close your right eye. If your finger appears to jump to the right, you are right eye dominant. Then open your right eye and close your left eye. If your finger remains in position in front of the object, you have confirmed your right eye dominance. Alternatively, if in the above test, upon closing your right eye your finger remains in position covering the object, you are left eye dominant. If you close your left eye instead and your finger appears to jump to the left you have confirmed your left eye dominance.
Eye dominance problems can be treated with
1. A severely-cast, crossover stock to bring the dominant eye in line with the gun's line of sight, 2. A patch over the dominant eye, or just a small piece of frosty Scotch tape on shooting glasses intercepting the dominant eye's line of sight, 3. Fully or partially closing the dominant eye, or 4. Learning to shoot from the dominant-eye shoulder.
While less convenient, methods that retain the use of both eyes better preserve the ability to perceive depth in three-dimensional space, a great benefit in wingshooting.

Wildcat Cartridge

A wildcat cartridge, or wildcat, is a custom cartridge for which ammunition and/or firearms are not mass-produced. These cartridges are often created in order to optimize a certain performance characteristic (such as the power, size or efficiency) of an existing commercial cartridge. Developing and using wildcat cartridges does not generally serve a purpose in military or law enforcement; it is more a hobby for serious shooting, hunting, gunsmithing and handloading enthusiasts, particularly in the United States. There are potentially endless amounts of different kinds of wildcat cartridges: one source of gunsmithing equipment has a library of over 6,000 different wildcat cartridges for which they produce equipment such as chamber reamers.

Reflector Sight

A generally non-magnifying optical device that has an optically collimated reticle, allowing the user to look through a partially reflecting glass element and see a parallax free cross hair or other projected aiming point superimposed on the field of view. Invented in 1900 but not generally used on firearms until reliably illuminated versions were invented in the late 1970s (usually referred to by the abbreviation "reflex sight").

SxS

Abbreviation for Side-By-Side.

Battery

Most firearms do not have literal batteries. But a firearm is said to be in battery when the breech is fully closed and locked, ready to fire. When the breech is open or unlocked, the gun is out of battery and no attempt should be made to fire it. A semi-automatic is out of battery when the slide fails to come all the way forward again after the gun has fired, making it dangerous or impossible to fire the next round. This condition can be created by a misfeed, a dirty gun, weak springs, the shooter's thumbs brushing against the slide, riding the slide, or any of several other causes.

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.

Laser Sight

A laser sight is an alternative sighting device which enables the shooter to quickly and accurately see where the firearm is aimed even when lighting or other conditions prevent using the gun's normal sights. Lasers may be located within the grips, hung from accessory rails at the front end of the gun, or placed within the firearm.

BUG

Abbreviation for 'Back Up Gun'

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

Hinge Pin

A short cylindrical rod of hardened steel running laterally near the front of the bar of a break-open gun's action around which the barrel hook revolves when the gun is opened. Over the decades, this pin and its complimentary hook can wear and a gun can sometimes "shoot loose" or "come off the face." The proper cure for this condition is to replace the hinge pin with a new one, slightly oversized, to compensate for wear on both itself and on the barrel hook.

GAP

Abbreviation for Glock Auto Pistol

Stovepipe

Failure of a spent case to completely eject from a semi-automatic firearm. The case usually stands on end while lodged in the ejection port.

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.

Night Sights

A type of iron sights that glow or shine in the dark, intended for use in low light conditions. Some night sights consist of tiny tubes of tritium, while others use a phosphorus paint.

SBS

Abreviation for short-barreled shotgun.

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.