Firearms Terminology Dictionary

A cartridge-name designation associated with designs developed for Colt semi-automatic pistols, as in .45 ACP or .380 ACP. It does not mean the firearm itself is automatic.

The mechanism that loads, locks, fires, extracts and ejects ammunition. Common action types include semi-automatic, bolt, lever, pump, break and revolver actions.

A gas block that lets the user regulate gas flow in a gas-operated firearm to tune cycling for ammunition, suppressor use or component changes.

Controls designed for practical operation from either side of the firearm, such as a safety selector, magazine release or charging handle.

The complete material fired or used in a firearm. A modern cartridge commonly includes a case, primer, propellant and projectile; a shotshell contains shot or a slug and related components.

An electrochemical surface treatment commonly used on aluminum firearm parts to improve corrosion and wear resistance.

A federal NFA classification with a specific statutory definition covering certain concealable weapons or devices that do not fit the other listed NFA categories. Classification depends on the exact design and configuration.

A rear iron sight with a small opening through which the shooter aligns the front sight.

A modular firearm platform derived from the ArmaLite rifle design. Civilian AR-15-pattern firearms are commonly semi-automatic and are available in many calibers and configurations.

A wide dovetail-style accessory rail commonly used with precision-rifle tripods, bipods and shooting supports.

The rear portion of a handgun grip. Replaceable backstraps allow grip size and shape to be adjusted.

A common term for general-purpose ammunition, often using a full-metal-jacket projectile rather than an expanding bullet.

The study of projectile behavior. Internal ballistics covers what happens inside the firearm, external ballistics covers flight, and terminal ballistics covers behavior at impact.

The tube through which the projectile travels. Its chamber, bore, rifling, length, contour and muzzle features affect function and performance.

The distance measured using the legally or technically specified method for the firearm type. Barrel length affects handling, velocity, compatibility and sometimes legal classification.

An informal term usually describing a full-power military-style rifle, commonly chambered in cartridges such as 7.62 NATO.

The AR-pattern assembly containing the bolt, carrier and related parts that locks, fires, extracts, ejects and cycles the action.

An operating system in which rearward case pressure and bolt mass or spring resistance cycle the action without a mechanically locked breech.

A manually operated action in which the shooter cycles a bolt to extract, eject, load and lock a cartridge.

The interior of a firearm barrel. In a rifled barrel it includes the lands and grooves.

An imaginary line running through the center of the barrel. Its height relative to the grip can influence perceived muzzle rise.

A preliminary process for aligning sights or an optic with the bore. Boresighting gets the setup close but does not replace live-fire zeroing.

An accessory originally designed to help stabilize a pistol. Legal classification depends on the complete firearm, how it is configured and current law; the accessory name alone does not decide classification.

A common cartridge-case material. Shooters also use “brass” as shorthand for fired cartridge cases, even when a case is made from another material.

An action that hinges open to expose the chamber or chambers for loading and unloading.

Shotshell ammunition loaded with multiple relatively large pellets, identified by sizes such as #4 buck, 00 buck or 000 buck.

A weighted component in many AR-pattern recoil systems that works with the action spring to control carrier movement and cycling.

The AR-pattern receiver extension that houses the buffer and action spring and commonly provides the mounting structure for a stock or brace.

The projectile portion of a cartridge. A bullet is not the complete cartridge.

A firearm layout that places the action and magazine behind the trigger, allowing a longer barrel in a shorter overall package.

A designation related to bore or projectile diameter. Caliber alone does not establish cartridge interchangeability; always use the exact ammunition marked for the firearm.

Tilting the firearm or optic away from vertical. Unintended cant can shift point of impact, especially at longer distances.

The number of cartridges a firearm or feeding device is designed to hold. Capacity restrictions vary by jurisdiction.

A relatively compact shoulder-fired firearm, often with a shorter barrel than a comparable full-length rifle.

A complete unit of ammunition. A centerfire cartridge typically includes the case, primer, propellant and bullet.

The ammunition component that holds the primer, propellant and projectile together. “Casing” is common informal usage.

A cartridge with the primer located in the center of the case head, unlike rimfire ammunition.

The portion of the firearm that supports and contains the cartridge for firing. Ammunition must match the chamber marking and manufacturer guidance.

A visible safety device inserted into the action or chamber area to indicate that the firearm is not loaded and the action is open.

A manually operated control used to retract the bolt or bolt carrier and prepare or clear the action.

A constriction at or near a shotgun muzzle that influences the spread of a shot pattern. Choke selection must be compatible with the barrel, load and projectile type.

A device that holds cartridges together, often to help load a magazine or firearm. It is not the same thing as a detachable magazine.

A red-dot design that seals the emitter inside the optic housing, helping prevent rain, lint or debris from blocking the light path.

The visible relationship between iron sights and an optic’s viewing window. Absolute and lower-third co-witness describe different apparent sight heights.

A barrel-manufacturing process that forms the bore and rifling by hammering barrel steel around a mandrel.

A muzzle device that redirects gas to reduce muzzle rise or movement. It may also change blast and sound experienced around the shooter.

Carrying a handgun so it is not openly visible. Eligibility, prohibited locations and other requirements vary by jurisdiction.

A bolt-action feeding system in which the extractor captures the cartridge rim as the round leaves the magazine and guides it into the chamber.

Ammunition whose primer residue can attract moisture and promote corrosion. Firearms used with it require prompt, appropriate cleaning.

The rotating revolver component containing multiple chambers for cartridges.

A handgun system in which the first trigger press may both cock and release the hammer, while later presses release a hammer cocked by slide movement.

An action in which each trigger press performs the double-action cycle rather than operating in a separate single-action mode.

A pistol-optic mounting pattern associated with the Leupold DeltaPoint Pro and certain compatible systems. Similar geometry does not eliminate the need to verify screws, recoil bosses and slide fit.

A gas-operated system commonly used in AR-pattern firearms in which gas travels through a gas tube into the carrier system to cycle the action.

A mounting method in which a suppressor or mount threads directly onto the firearm barrel without a separate quick-detach muzzle device.

Recorded ballistic and sight-adjustment data used to predict holds or corrections at different distances and conditions.

The angular size of a red-dot reticle, commonly stated in MOA. A larger dot is usually quicker to see; a smaller dot covers less of the target.

A trigger action that performs two functions, commonly cocking and releasing a hammer during the same trigger press.

A self-contained trigger module intended to simplify installation in a compatible firearm.

Practicing firearm manipulation and trigger control without live ammunition. Confirm the firearm manufacturer permits it and follow a deliberate unloaded-practice safety process.

An informal quality description suggesting equipment is designed for demanding professional use. It is not a universal test standard.

Items carried routinely for daily preparedness, which may include a lawfully carried handgun, holster, light, medical equipment and other tools.

The general direction and distance that fired cases leave a semi-automatic firearm. It can provide clues about gas, recoil-system or ammunition behavior but is not a diagnosis by itself.

The opening through which a cartridge or fired case exits the action.

The component that pushes or strikes the case so it exits the firearm after extraction.

Vertical sight or optic adjustment that moves point of impact up or down.

The component that grips the cartridge case and pulls it from the chamber.

The three-dimensional area behind a magnified optic where the shooter can see a full sight picture.

The distance between the shooter’s eye and the rear lens at which a full sight picture is visible.

The trigger, hammer or striker interfaces, sear and related parts that control firing and reset.

A federal license authorizing specific firearms business or collecting activities. In common usage, “an FFL” often means the person or business operating under the license.

A transfer handled by a Federal Firearms Licensee, commonly involving receipt of the firearm, identity verification, required records, ATF Form 4473 and a background check when applicable.

A general term for a weapon that expels a projectile through an explosive process. Federal and state laws use specific definitions that can also cover certain frames, receivers, silencers, destructive devices or weapon parts kits.

A barrel that remains substantially stationary during the operating cycle. Many rifles, PCCs and rimfire firearms use fixed barrels.

A manufacturer-approved component that prevents a pistol suppressor booster from moving when used on a compatible fixed-barrel host.

A muzzle device designed to reduce visible muzzle flash. It is different from a sound suppressor.

An informal description for a cartridge or firearm combination with relatively little trajectory drop over the distances being discussed.

The location of a riflescope reticle within the optical system. In a first-focal-plane scope, reticle subtensions scale with magnification; in a second-focal-plane scope, they remain visually constant.

The mounting interface on the bottom of an optic, including screw locations, recoil-lug geometry and physical contact surfaces.

A receiver produced from metal shaped under pressure before final machining. Forged, billet and cast describe manufacturing methods rather than guaranteed quality levels.

An ATF application used when a person or entity seeks approval to make and register a firearm under the NFA when that process applies.

An ATF form used for certain tax-exempt transfers of NFA firearms between qualified federal licensees or government entities when applicable.

An ATF application used for the transfer and registration of an NFA firearm to a transferee when that process applies.

The federal Firearms Transaction Record completed for many transfers from an FFL to an unlicensed person. It documents the transaction and buyer eligibility questions; it is not a firearm training certificate.

A handguard designed not to contact the barrel, helping reduce changes in barrel movement caused by sling, support or accessory pressure.

A bullet construction in which a harder metal jacket covers most of the lead core, commonly used for training and general-purpose ammunition.

A component that captures gas from a barrel port and routes it into a firearm’s gas-operating system.

The AR-pattern bolt-carrier component that receives gas from the gas tube.

An operating system that uses propellant gas to drive a piston, which transfers energy to cycle the action.

The approximate distance between an AR-pattern chamber and gas port, commonly described as pistol, carbine, mid-length or rifle.

A traditional measurement used for most shotgun bore sizes. Gauge is not interchangeable with caliber, and smaller gauge numbers generally indicate larger bores.

A unit of mass used for bullets and propellant. One grain equals 1/7,000 of a pound. Bullet weight does not describe powder charge.

The angle of a firearm grip relative to the bore or frame, affecting wrist position and how the sights present.

The measured spread of multiple shots on a target, typically measured between the centers of the two farthest-apart impacts.

A person who professionally inspects, repairs, modifies or builds firearms. Licensing requirements depend on the work and business activity performed.

An abbreviation for Global War on Terror, also used informally to describe equipment, rifle setups and aesthetics associated with the post-September 11 military era.

A firing system that uses an external or internal hammer to strike a firing pin or primer interface.

The portion surrounding or positioned near a long gun’s barrel that provides a protected support-hand area and often accessory mounting locations.

A firearm designed to be fired with one hand. Federal and state statutes may define the term more specifically for legal purposes.

The distance from the closed breech face to the chamber surface that stops forward movement of the cartridge. Correct headspace is essential for safe, reliable operation.

The vertical distance between the bore axis and the sighting axis. It affects close-range offset and trajectory calculations.

A projectile with a cavity in the nose designed to promote controlled expansion under intended conditions.

A compact pistol-optic footprint used by models such as the Holosun 407K and 507K. It is related to but not automatically identical with every RMSc-pattern cut.

Features that resist unintended firearm removal. Passive retention uses fit or friction; active retention requires a deliberate release action.

The firearm on which a suppressor, optic or accessory is installed.

The common 1.375x24 rear suppressor mounting interface often called HUB or Bravo. It accepts compatible suppressor-side mounts but does not determine barrel thread, caliber or complete-system compatibility.

Mechanical front and rear sights used to align a firearm with the target.

A handgun stance in which both arms extend toward the target and the shoulders remain generally square, forming a triangle-like shape.

An expanding bullet design that combines a hollow nose cavity with an outer metal jacket.

Dead Air’s quick-detach suppressor mounting ecosystem using a compatible suppressor-side adapter and barrel-mounted muzzle device.

An open-source handguard accessory interface identified by keyhole-shaped slots. It has been largely overtaken in popularity by M-LOK.

A rigid thermoplastic commonly formed into firearm holsters, magazine carriers and equipment shells.

The raised and recessed portions of conventional rifling that engage the projectile and impart spin.

The distance from the trigger face to the rear surface of the stock or other shoulder-contact point.

A manually operated action cycled by moving a lever, commonly located around or behind the trigger guard.

A holster designed around a specific firearm and weapon-mounted-light combination. Light and gun model compatibility are both critical.

A muzzle device intended to direct blast and sound energy more forward rather than primarily to the sides.

A general term for shoulder-fired firearms such as rifles and shotguns. Specific legal definitions and age requirements can depend on firearm type and jurisdiction.

The lower portion of an AR-pattern firearm that houses the fire-control group and magazine well. Under current federal definitions, the AR-pattern lower is the regulated receiver.

A low-power variable optic, commonly offering a near-1x low setting and adjustable magnification for close-to-intermediate use.

Texas’s handgun carry license. Permitless carry did not eliminate the LTC program, and an LTC can provide benefits that unlicensed carry does not.

A standardized negative-space accessory mounting system developed by Magpul for attaching compatible rails and accessories to handguards.

A feeding device that stores cartridges and presents them for loading into the chamber. Magazines may be detachable or fixed.

The opening or structure that accepts a magazine. An added flared magwell can help guide reloads.

A cartridge-name designation generally suggesting greater case capacity or performance relative to another cartridge. It is not a universal technical threshold.

A user-operated control intended to block or interrupt part of the firing sequence. It does not replace safe handling.

An angular unit used for optic adjustments and reticles. One milliradian subtends 10 centimeters at 100 meters or approximately 3.6 inches at 100 yards.

A requirement or dimensional standard associated with a military specification. In commercial marketing it often indicates compatibility, not automatically premium quality.

An angular measurement equal to 1/60 of a degree. One MOA subtends about 1.047 inches at 100 yards and is often rounded to one inch for quick calculations.

A removable internal chassis or fire-control assembly used in some modular pistols. On certain designs, this assembly is the serialized frame under federal definitions.

A barrel that moves during the firing cycle, common in recoil-operated semi-automatic pistols. Suppressor use commonly requires a compatible piston and booster system.

The open end of the barrel from which the projectile exits.

A muzzle device that redirects propellant gas to reduce felt recoil. It can increase perceived blast and concussion around the shooter.

An attachment at the barrel muzzle, such as a flash hider, brake, compensator or suppressor mount.

Calculated projectile energy at the muzzle, commonly expressed in foot-pounds. It is only one part of cartridge performance.

Projectile speed as it leaves the muzzle, commonly measured in feet per second. Actual velocity varies with barrel, ammunition and conditions.

A federal statute associated with specified firearm categories, registration and transfer or making procedures. Court decisions, legislation and agency guidance can affect how particular items are treated, so current requirements must be verified.

Industry shorthand for a firearm or device regulated—or historically treated as regulated—under the National Firearms Act. It is not the Act’s primary defined term.

The FBI’s national system used to check records that may disqualify a person from receiving a firearm. An FFL or state point of contact initiates the check when required.

A spring-loaded suppressor component that allows the suppressor to move independently enough for many recoil-operated pistol barrels to cycle.

Iron sights designed to remain visible in reduced light, commonly through tritium, fiber-optic or photoluminescent elements.

A laboratory-derived rating used for hearing protection. Real-world protection depends on correct fit, use and the shooting environment.

Carrying a firearm so it is visible. Eligibility, holster requirements, prohibited locations and other rules vary by jurisdiction.

A red-dot design with an exposed light path between the emitter and lens. It is often lighter and more compact than a comparable enclosed optic.

Machining on a firearm that accepts an optic directly or through a plate system. The exact cut determines compatible footprints and hardware.

A firearm prepared to accept an optic through a particular cut, plate or mounting system. It does not mean every optic fits.

An informal description for a gas-operated firearm receiving more gas drive than needed for the setup, potentially producing harsh cycling, early extraction or excess wear.

The firearm’s complete end-to-end length measured under the method required for the specific technical or legal purpose. Measurement rules can affect classification.

Apparent reticle movement relative to the target when the shooter’s eye changes position. “Parallax free” is normally true only at a specified distance or within practical tolerances.

A shoulder-fired or carbine-style firearm chambered for a cartridge commonly associated with handguns.

A term used for compact defensive firearms or military weapon systems. Commercial use is informal and does not establish a legal firearm classification.

A standardized rail with defined slot dimensions used to attach optics, lights and accessories.

A handgun designed to be fired with one hand and having a chamber integral with or permanently aligned with the bore. Exact legal definitions may differ by law and context.

In pistol suppressor mounting, the threaded component that matches the barrel and works within the booster assembly. The term can also describe part of a gas-piston operating system.

Griffin Armament’s taper-mount ecosystem, using a suppressor-side Plan A adapter and compatible barrel-mounted Griffin taper device.

A taper-mount ecosystem associated with Q’s Cherry Bomb pattern and compatible aftermarket muzzle devices and suppressor-side adapters.

The exact location at which the sights or optic are aligned.

The location where the projectile strikes relative to the point of aim.

The ignition component in a cartridge or shotshell that initiates propellant combustion when struck or otherwise activated.

The object or objects launched through the barrel, such as a bullet, slug or shot pellets.

Special ammunition loaded to a specified higher pressure for controlled testing of firearms or components. It is not general-use ammunition.

The measured force required to move a trigger through the release point under the stated test method.

A manually operated action cycled by sliding the fore-end to extract, eject, cock and load.

A mounting feature designed for rapid attachment or removal, often without loose tools. QD does not guarantee compatibility between different ecosystems.

A socket that accepts a push-button sling swivel for quick sling attachment and removal.

A suppressor attachment system using a compatible muzzle device and suppressor-side adapter to speed installation and removal.

An informal term for a firearm heavily configured for speed-oriented competition, often with tuned controls, compensators and large-window optics.

A regulated firearm component under federal law. The identified receiver differs by design; for example, an AR-pattern lower and certain internal pistol chassis can be the regulated component.

Rearward firearm movement resulting from firing. Perceived recoil depends on firearm weight, action, stock or grip fit, ammunition and muzzle devices.

How recoil force is delivered over time. Two setups can have similar total recoil energy but feel different because the impulse shape differs.

A non-magnified electronic sight that projects a reticle into the shooter’s view for target-focused aiming.

The aiming pattern seen through an optic, such as a dot, circle-dot, crosshair, ranging grid or illuminated center point.

A handgun with a rotating cylinder containing multiple chambers that align in sequence with the barrel.

A shoulder-fired firearm designed to fire a single projectile through a rifled bore for each trigger function. Legal definitions include additional details and can affect configuration.

Spiral features inside a barrel that spin-stabilize a projectile. Conventional rifling uses lands and grooves; other forms include polygonal rifling.

A cartridge with priming compound distributed in the rim of the case, as with .22 LR.

A widely supported standard-width pistol-optic mounting pattern associated with the Trijicon RMR and several compatible optics.

Trijicon’s compact RMRcc mounting interface. It is not the same as the standard RMR or Shield RMSc footprint.

A compact pistol-optic mounting pattern associated with the Shield RMSc. Related micro footprints may still differ in recoil bosses and screw requirements.

Common shorthand for one complete cartridge or shotshell. It can also describe one firing sequence or stage in other contexts.

A person responsible for supervising range safety procedures, commands and activity within the scope of the range’s rules.

An informal term for a firearm that is rarely used and is primarily stored, displayed or preserved in excellent condition.

A federal classification generally involving a rifle with a barrel under 16 inches or a weapon made from a rifle with an overall length under 26 inches. Configuration and measurement rules matter, and current requirements must be verified.

A federal classification generally involving a shotgun with a barrel under 18 inches or a weapon made from a shotgun with an overall length under 26 inches. Configuration and measurement rules matter.

An action that fires one cartridge per trigger function and automatically cycles to load the next cartridge.

Common shorthand for shotgun ammunition. In precise usage, “shotshell” identifies the complete loaded unit.

Multiple spherical projectiles loaded in a shotshell, identified by standardized size designations.

A shoulder-fired firearm designed to fire through a smooth bore, commonly using shotshells containing shot or a single slug. Legal definitions include additional details.

The distance between front and rear iron sights. A longer radius generally makes angular alignment errors easier to see.

A trigger action that performs one primary function, commonly releasing a previously cocked hammer or striker.

The reciprocating upper assembly on many semi-automatic pistols that houses the barrel, recoil system and firing components.

A control that can hold a pistol slide open and, on many designs, release it. Manufacturer terminology varies.

A single projectile designed to be fired from a shotgun. Slug type must be compatible with the firearm, barrel and choke.

A qualified federal firearms licensee who has paid the special occupational tax associated with importing, manufacturing or dealing in NFA firearms, as applicable to the license and activity.

An underpowered discharge that can leave a projectile lodged in the barrel. Stop firing immediately if a squib is suspected and have the firearm safely inspected.

A component designed to support a shoulder-fired firearm against the shooter’s body. Adding or changing a stock can affect firearm configuration and legal classification.

A firing system using a spring-driven striker rather than a separate hammer.

A commercial size category for relatively small handguns. Dimensions are not standardized across manufacturers.

Ammunition intended to keep projectile velocity below the local speed of sound under expected conditions. Actual velocity varies with barrel length, temperature and lot.

A device designed to reduce the sound signature of a firearm by controlling propellant gases. It does not make firing silent, and its federal or state legal treatment must be verified under current law.

A marketing description indicating some factory features support suppressor use, often a threaded barrel and suitable sights or gas settings. It does not guarantee compatibility with every suppressor.

An aiming method in which visual attention remains on the target while the red-dot reticle is superimposed in the sight picture.

The diameter and spacing system of barrel or mount threads, such as 1/2x28 or 5/8x24. Matching thread pitch does not by itself prove bore or device compatibility.

A barrel with external muzzle threads for compatible devices. Thread pitch, shoulder geometry, bore alignment and firearm operation must all be considered.

A rapid suppressor attachment system using three barrel-side lugs and a compatible suppressor-side mount, commonly seen on MP5-pattern firearms and PCCs.

The manufacturer-specified rotational tightening force for a fastener. Correct units, tools, sequence and thread preparation matter.

The curved flight path of a projectile after it leaves the muzzle.

The control operated by the shooter to initiate the firing sequence.

The point in trigger movement at which the sear releases and the firing sequence begins.

The point during forward trigger travel at which the firing mechanism re-engages for the next shot.

The distance over which rifling makes one complete revolution, such as 1 turn in 7 inches. Twist rate influences projectile stability.

An informal description for a gas-operated firearm receiving insufficient gas drive to cycle reliably with the current ammunition and configuration.

The AR-pattern assembly or housing that supports the barrel and operating components. On a standard AR-15 pattern, it is not the federally regulated receiver by itself.

An FBI NICS process that can help eligible individuals address recurring record-matching issues. Approved participants may receive a Unique Personal Identification Number, or UPIN.

The speed of a projectile, commonly expressed in feet per second. Published velocity depends on the test barrel and conditions.

A grip intended to be held vertically from a firearm’s fore-end. Installing one can affect federal classification depending on the firearm and configuration.

A flat-front handgun bullet designed to cut clean, round holes in paper targets.

A light attached to a firearm for target identification and illumination. A mounted light does not replace a handheld light or safe identification practices.

Horizontal sight or optic adjustment that moves point of impact left or right.

Small alignment marks placed across fasteners and adjacent surfaces to help reveal visible movement after installation.

The smaller center scoring area inside the highest-value portion of many paper targets, used for tie-breaking or precision scoring.

Dead Air’s threaded taper suppressor mounting ecosystem, using compatible barrel-side muzzle devices and suppressor-side adapters.

A meter is approximately 1.094 yards. Confirm the unit used for targets, ballistic data and optic adjustments.

Angular deviation of a projectile’s longitudinal axis from its direction of travel. Excessive yaw can affect stability and impact shape.

The relationship established between point of aim and point of impact at a chosen distance.

The distance at which the shooter confirms the chosen relationship between point of aim and point of impact.