Gun Terms Glossary

Terms are listed alphabetically, with caliber names that start with a number grouped first. Tap a letter to jump to it.

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.22 LR (.22 Long Rifle)

A small, low-recoil rimfire cartridge. It is inexpensive and quiet compared with centerfire rounds, which makes it the most popular choice for plinking, small-game hunting and teaching new shooters.

.223 Remington

A small-bore centerfire rifle cartridge used in many AR-15-style rifles. It is dimensionally similar to 5.56 NATO but loaded to slightly lower pressure; check your barrel markings to see which your rifle is rated for.

.30-06 Springfield

A classic American rifle cartridge introduced in 1906 and still widely used for hunting large game such as elk and deer.

.308 Winchester

A popular centerfire rifle cartridge for hunting and long-range target shooting. Its military counterpart is 7.62x51mm NATO.

.380 ACP

A short pistol cartridge, also called 9mm Short or 9mm Kurz, common in small, lightweight carry pistols. It has less recoil and less energy than 9mm Luger.

.45 ACP

A large-diameter pistol cartridge designed by John Browning for the 1911 pistol. It fires a heavy, relatively slow bullet and remains popular for defense and target shooting.

5.56x45mm NATO

The standard military cartridge for the M16/M4 family and a common chambering for AR-15-style rifles. Rifles chambered in 5.56 can generally fire .223 Remington, but not always the other way around.

6.5 Creedmoor

A modern rifle cartridge known for flat trajectory, low recoil and good wind resistance, which has made it a favorite for long-range target shooting and hunting.

9mm Luger (9x19mm)

The most popular handgun cartridge in the United States. It offers manageable recoil, high magazine capacity and widely available, affordable ammunition.

10mm Auto

A powerful semi-automatic pistol cartridge with more energy and recoil than 9mm or .40 S&W, often chosen for hunting and backcountry carry.

12 Gauge

The most common shotgun size. Gauge numbers run backward, so a 12 gauge has a larger bore than a 20 gauge.

A

Action

The mechanism of a firearm that loads, fires and ejects cartridges. Common types are bolt, lever, pump, semi-automatic and revolver actions.

Ammunition

The complete package fired from a gun. For most guns this is a cartridge made of a case, primer, powder and bullet; for shotguns it is a shell.

Aperture Sight

Also called a peep sight. A rear sight with a small ring you look through; your eye naturally centers the front sight in the ring, which makes aiming quick and precise.

AR-15

A lightweight, modular semi-automatic rifle design originally developed by ArmaLite. "AR" stands for ArmaLite Rifle, not "assault rifle." It is one of the best-selling rifles in the U.S.

ATF

The Bureau of Alcohol, Tobacco, Firearms and Explosives, the federal agency that licenses firearm dealers and manufacturers and enforces federal firearm laws.

B

Ballistics

The study of how a bullet behaves: inside the gun (internal), in flight (external) and when it hits the target (terminal).

Barrel

The metal tube the bullet travels through when fired. Barrel length affects velocity, handling and, for some guns, legal classification.

Bolt Action

A manually operated action where the shooter lifts and pulls a bolt handle to eject a spent case and pushes it forward to load the next round. Known for accuracy and reliability.

Bore

The inside of the barrel. Bore diameter is closely related to caliber.

Bullet

The projectile that leaves the barrel. People often say "bullet" when they mean the whole cartridge, but technically the bullet is only the part that flies downrange.

Buttstock

The rear part of a rifle or shotgun that rests against the shooter's shoulder.

C

Caliber

The approximate diameter of a bullet or bore, given in inches (.45) or millimeters (9mm). It is also used loosely to mean a specific cartridge.

Cartridge

A single unit of ammunition: case, primer, powder and bullet assembled together. Also called a round.

Case (Casing)

The container, usually brass, steel or aluminum, that holds the primer, powder and bullet together. It is ejected after firing.

Centerfire

Ammunition with the primer in the center of the case base. Nearly all handgun and rifle cartridges larger than .22 are centerfire.

Chamber

The rear part of the barrel that holds the cartridge when it is ready to fire.

Choke

A constriction at the muzzle of a shotgun barrel that controls how quickly the shot pattern spreads. Many shotguns accept interchangeable choke tubes.

Clip

A strip or clip that holds cartridges together for loading into a magazine, such as an M1 Garand en bloc clip or a stripper clip. It is often confused with a magazine, which has its own spring and feeds rounds into the gun.

Concealed Carry

Carrying a handgun hidden from view on your person. Rules vary by state, and many states require or offer a permit (CCW, CHL or CPL).

Cylinder

The rotating part of a revolver that holds cartridges in separate chambers, typically five to eight.

D

Double Action (DA)

A trigger that both cocks and releases the hammer in one pull. Double-action triggers are longer and heavier than single-action triggers.

DA/SA (Double-Action/Single-Action)

A pistol whose first shot is fired double action and later shots single action, because the slide cocks the hammer after each shot. The Beretta 92 is a well-known example.

Dry Fire

Practicing trigger pull and sight alignment with an unloaded gun. Always confirm the gun and room are free of ammunition first, and check whether your model needs snap caps.

E

Ejector

The part that kicks the spent case out of the gun after the extractor pulls it from the chamber.

Elevation

The vertical adjustment on a sight or scope that moves the point of impact up or down.

Extractor

A small hook that grips the rim of the case and pulls it out of the chamber.

Eye Relief

The distance your eye can be from a scope's rear lens and still see the full picture. Longer eye relief helps keep the scope from hitting you under recoil.

F

FFL (Federal Firearms License)

A license issued by the ATF to people and businesses that deal in or make firearms. When you buy a gun online, it ships to an FFL dealer, who runs the background check and transfers it to you.

Field of View (FOV)

How wide an area you can see through a scope or binocular, usually listed in feet at 100 yards. Higher magnification means a narrower field of view.

FMJ (Full Metal Jacket)

A bullet with a soft lead core covered by a harder metal jacket, usually copper. FMJ is the standard affordable choice for range practice.

Front Sight

The sight at the muzzle end of the gun that you line up with the rear sight and the target.

G

Gauge

The bore size of a shotgun, based on how many lead balls of that diameter make a pound. Common gauges are 12, 20 and 28; the .410 bore is the exception and is measured in inches.

Grain (gr)

A unit of weight used for bullets: 7,000 grains equal one pound. A "115 gr" 9mm bullet is lighter than a "147 gr" one.

Grip

The part of a handgun you hold, or the panels attached to it. On rifles it usually refers to the pistol grip behind the trigger.

H

Hammer

The part that strikes the firing pin or primer to fire the gun. It can be exposed, like on a 1911 or most revolvers, or internal.

Holographic Sight

A non-magnified sight that projects a reticle using a laser hologram, popularized by EOTech. It works with both eyes open, like a red dot.

Holster

A case for carrying a handgun. A good holster covers the trigger guard completely and holds the gun securely. Styles include IWB (inside the waistband) and OWB (outside the waistband).

I

Iron Sights

Basic metal sights, usually a front post or blade and a rear notch or aperture, with no glass or electronics.

J

JHP (Jacketed Hollow Point)

A bullet with a cavity in the nose designed to expand on impact. JHP is the common choice for self-defense handgun ammunition because it is designed to slow down in the target and reduce overpenetration.

L

Lever Action

A manual action worked by a lever under the receiver, behind the trigger. Classic cowboy-era rifles from Winchester, Marlin and Henry use it.

LPVO (Low Power Variable Optic)

A riflescope that zooms from 1x (true or near-true view) up to a modest magnification such as 6x, 8x or 10x, letting one optic work up close and at distance.

M

Magazine

A container with a spring and follower that holds cartridges and feeds them into the action. It can be detachable (like a pistol magazine) or built into the gun. Often mistakenly called a clip.

Magnification

How many times larger a scope makes the target look. A 4x scope makes a target at 400 yards look like it is 100 yards away.

MOA (Minute of Angle)

An angle equal to 1/60 of a degree, roughly 1 inch at 100 yards. It is used to describe accuracy (a "1 MOA rifle") and scope adjustments ("1/4 MOA clicks"), and the size of red-dot reticles.

MRAD (Milliradian, Mil)

An angular measurement equal to 1/1,000 of a radian, about 3.6 inches at 100 yards. Many long-range scopes use mils for both reticle markings and adjustments, typically in 0.1 mil clicks.

Muzzle

The front end of the barrel where the bullet exits. Always keep the muzzle pointed in a safe direction.

Muzzle Velocity

The speed of the bullet as it leaves the barrel, usually listed in feet per second (fps) on ammunition boxes.

N

NFA (National Firearms Act)

A 1934 federal law that regulates certain categories of firearms and devices, such as machine guns, short-barreled rifles and shotguns, and suppressors. Covered items must be registered with the ATF and require an approved application and tax stamp before transfer.

NICS

The FBI's National Instant Criminal Background Check System, which licensed dealers use to check a buyer's eligibility before a firearm transfer.

O

Optics-Ready

A pistol whose slide is cut or plated to mount a small red-dot sight. Often abbreviated OR or MOS, depending on the maker.

Over/Under

A double-barreled shotgun with one barrel stacked on top of the other, popular for clay sports and bird hunting. A side-by-side places the barrels next to each other.

P

Parallax

The apparent shift of a scope's reticle against the target when you move your eye. Scopes with parallax adjustment let you correct it for a given distance.

Picatinny Rail

A standardized mounting rail (MIL-STD-1913) with evenly spaced slots for attaching optics, lights and other accessories.

Pistol

A handgun, most often one with the chamber built into the barrel, like a semi-automatic, as opposed to a revolver.

Primer

The small, impact-sensitive component in the base of a cartridge that ignites the powder when struck by the firing pin.

Pump Action

A manual action worked by sliding the fore-end back and forward to eject and load. Most common on shotguns.

R

Recoil

The backward push of a gun when it is fired. Heavier guns and lighter loads generally recoil less.

Red Dot Sight

A non-magnified optic that shows an illuminated dot on a lens. You put the dot on the target and shoot, which is fast and works with both eyes open.

Reticle

The aiming pattern inside an optic, such as crosshairs, a dot or a ranging grid.

Revolver

A handgun that holds cartridges in a rotating cylinder. Revolvers are mechanically simple and do not depend on ammunition power to cycle.

Rifling

Spiral grooves cut or formed inside a barrel that spin the bullet for stability and accuracy.

Rimfire

Ammunition with priming compound in the rim of the case instead of a separate primer, such as .22 LR and .22 WMR. Rimfire cases are not reloadable.

Round

Another word for one cartridge or shotgun shell.

S

Safety

A mechanical device that helps prevent the gun from firing. It can be manual (a lever you switch) or passive (internal or trigger safeties). A safety never replaces safe handling.

Semi-Automatic

A gun that fires one round per trigger pull and uses the energy of each shot to eject the empty case and load the next round.

Shotgun

A long gun usually fired from the shoulder that shoots shells containing many small pellets (shot) or a single slug.

Sight Radius

The distance between the front and rear sights. A longer sight radius makes small aiming errors easier to see.

Single Action (SA)

A trigger that only releases a hammer or striker that is already cocked. Single-action triggers are typically short and light, as on a 1911.

Slide

The top part of a semi-automatic pistol that moves back and forth with each shot, ejecting the spent case and chambering a new round.

Striker-Fired

A pistol that uses a spring-loaded striker instead of a hammer to fire, giving a consistent trigger pull every shot. Glock, Sig P320 and S&W M&P pistols are striker-fired.

T

Trigger

The lever you press to fire the gun. Keep your finger off the trigger until your sights are on the target and you have decided to shoot.

Trigger Pull

The force needed to fire the gun, usually measured in pounds, along with how the trigger feels as it moves (take-up, break and reset).

Twist Rate

How quickly the rifling spins the bullet, written as one turn in a number of inches, such as 1:7 or 1:10. Faster twist rates stabilize longer, heavier bullets.

W

Windage

The horizontal adjustment on a sight or scope that moves the point of impact left or right. It also refers to the effect of wind on a bullet's flight.

Z

Zero

Adjusting your sights or optic so the point of aim matches the point of impact at a chosen distance, such as a 50-yard or 100-yard zero.