Ask a QuestionUnansweredGear ReviewsBuyer's GuidesToolsPollsSetupsRate My BuildReportsGlossaryTopicsCommunitySubmitAbout
Learn the Lingo

Gun Terms Glossary

Plain-English definitions of the firearm terms every shooter runs into — from MOA and twist rate to NFA and appendix carry. New to guns or brushing up, start here.

OpticsAmmoMechanicsCarryLegalSafetyShooting

Optics

Co-WitnessAligning a red dot with backup iron sights so both can be used together — either with the irons centered in the dot (absolute) or lower (lower 1/3).MIL (Milliradian)An angular unit equal to 1/1000th of a radian — about 3.6 inches at 100 yards (or 10 cm at 100 m) — used for ranging and scope adjustments.MOA (Minute of Angle)An angular measurement equal to 1/60th of a degree — about 1.047 inches at 100 yards — used for scope adjustments and group sizes.ParallaxAn optical error where the reticle appears to shift against the target as you move your eye — corrected with a parallax adjustment on higher-power scopes.Red Dot SightA non-magnifying electronic sight that projects an illuminated aiming dot, allowing fast target acquisition with both eyes open.

Ammo

+P (Overpressure Ammunition)Ammunition loaded to higher-than-standard pressure for more velocity and energy — only safe in firearms rated for it.Ballistic Coefficient (BC)A number describing how well a bullet resists air drag — higher BC means a flatter trajectory and less wind drift.CaliberThe bore diameter of a firearm (and the cartridge it fires), usually given in inches or millimeters — e.g., .45 or 9mm.FMJ (Full Metal Jacket)A bullet with a soft lead core fully encased in a harder metal jacket — inexpensive, reliable target and practice ammunition.GaugeThe bore-size measurement for shotguns, based on how many lead balls of bore diameter make a pound — lower gauge means a bigger bore.JHP (Jacketed Hollow Point)A defensive bullet with a hollow cavity in the nose designed to expand on impact, increasing stopping power and limiting over-penetration.Muzzle EnergyThe kinetic energy a bullet carries as it leaves the barrel, measured in foot-pounds — a common proxy for a load's power.Muzzle VelocityThe speed of a bullet as it leaves the barrel, measured in feet per second (fps) — a major driver of trajectory and energy.

Mechanics

BoreThe hollow interior of a barrel through which the bullet travels; its diameter defines caliber or gauge.CyclingThe full sequence a self-loading firearm performs to fire, extract, eject, and chamber the next round.Double Action (DA / DA-SA)A trigger that both cocks and releases the hammer in one pull — heavier and longer than single action, often paired as DA/SA.Gas SystemThe mechanism in a semi-automatic firearm that taps propellant gas to cycle the action — common AR-15 lengths are carbine, mid, and rifle.Magazine vs. ClipA magazine is a spring-loaded ammo-feeding device; a clip merely holds rounds together to load a magazine or cylinder. They are not the same.Malfunction (FTF / FTE)Any interruption in a firearm's cycle — common types include failure to feed, failure to fire, failure to extract, and the 'stovepipe'.RiflingThe spiral grooves cut or formed into a barrel's bore that spin the bullet for stability — the raised areas are 'lands', the recessed are 'grooves'.Single Action (SA)A trigger that performs only one action — releasing an already-cocked hammer — giving a short, light pull.Striker-FiredA pistol design that uses a spring-loaded internal striker instead of an external hammer to ignite the primer.SuppressorA muzzle device that reduces the sound, flash, and recoil of a gunshot by slowing and cooling escaping gases — an NFA-regulated item.Twist RateHow fast the rifling spins a bullet, expressed as one turn in N inches (e.g., 1:7) — it must match bullet weight for stable flight.

Carry

Appendix Carry (AIWB)Carrying a holstered handgun inside the waistband at the front of the body, near the appendix (around the 1 o'clock position).EDC (Everyday Carry)The gun and gear a person carries on their person every day for self-defense and daily use.IWB vs. OWBHolster positions — Inside the Waistband (IWB) tucks the gun inside your pants for concealment; Outside the Waistband (OWB) rides on the belt.PrintingWhen the outline of a concealed firearm shows through clothing, revealing that you're armed.

Safety

Negligent Discharge (ND / AD)An unintended firing of a gun — 'negligent' when caused by human error, 'accidental' when due to a genuine mechanical failure.The Four Rules of Gun SafetyThe foundational safety rules: treat every gun as loaded, never point at anything you won't destroy, keep your finger off the trigger until ready, and know your target and beyond.

Shooting

Dry FirePracticing trigger control and gun handling with an unloaded firearm and no ammunition present.HoldoverAiming above the target to compensate for bullet drop at distances beyond your zero, instead of dialing the scope.Limp-WristingA shooter-induced pistol malfunction caused by a loose grip that lets the frame move too much for the slide to cycle fully.RecoilThe rearward force you feel when a gun fires, a reaction to the bullet and gases being driven forward (Newton's third law).Trigger ResetThe short distance the trigger must travel forward after a shot before it will fire again — a key to fast, accurate shooting.Zero (Sighting In)The distance at which a gun's sights are adjusted so the point of aim matches the point of impact.