* Courtesy NRA-ILA

ACTION
The working mechanism of a firearm. Various types exist, including single-shots, multi-barrels, revolvers, slide- or pump-actions, lever-actions, bolt-actions, semi-automatics and automatics.

AIRGUN
Not a firearm but a gun that uses compressed air or CO2 to propel a projectile. Examples: BB gun, pellet gun, CO2 gun.

AMMUNITION
This generally refers to the assembled components of complete cartridges or rounds i.e., a case or shell holding a primer, a charge of propellant (gunpowder) and a projectile (bullets in the case of handguns and rifles, multiple pellets or single slugs in shotguns). Sometimes called "fixed ammunition" to differentiate from components inserted separately in muzzleloaders.

ANTIQUE
By federal definition, a firearm manufactured prior to 1899 or a firearm for which ammunition is not generally available or a firearm incapable of firing fixed ammunition.

ARMOR-PIERCING AMMUNITION
By federal definition, "a projectile or projectile core which may be used in a handgun and which is constructed entirely (excluding the presence of traces of other substances) from one or a combination of tungsten alloys, steel, iron, brass, bronze, beryllium copper, or depleted uranium. Such term does not include shotgun shot required by... game regulations for hunting purposes, a frangible projectile designed for target shooting, a projectile which the Secretary finds is primarily intended to be used for sporting purposes, or any other projectile or projectile core which the Secretary finds is intended to be used for industrial purposes, including a charge used in an oil and gas well perforating device."

ASSAULT RIFLE
By U.S. Army definition, a selective-fire rifle chambered for a cartridge of intermediate power. If applied to any semi-automatic firearm regardless of its cosmetic similarity to a true assault rifle, the term is incorrect.

ASSAULT WEAPON
Any weapon used in an assault (see WEAPON).

AUTOMATIC
A firearm designed to feed cartridges, fire them, eject their empty cases and repeat this cycle as long as the trigger is depressed and cartridges remain in the feed system. Examples: machine guns, submachine guns, selective-fire rifles, including true assault rifles.

AUTOMATIC PISTOL
A term used often to describe what is actually a semi-automatic pistol. It is, technically, a misnomer but a near-century of use has legitimized it, and its use confuses only the novice.

BALL
Originally a spherical projectile, now generally a fully jacketed bullet of cylindrical profile with round or pointed nose. Most commonly used in military terminology.

BLACKPOWDER
The earliest type of firearms propellant that has generally been replaced by smokeless powder except for use in muzzleloaders and older breechloading guns that demand its lower pressure levels.

BLANK CARTRIDGE
A round loaded with blackpowder or a special smokeless powder but lacking a projectile. Used mainly in starting races, theatrical productions, troop exercises and in training dogs.

BOLT-ACTION
A gun mechanism activated by manual operation of the breechblock that resembles a common door bolt.

BORE
The interior of a firearm's barrel excluding the chamber.

BRASS
A synonym for expended metallic cartridge cases.

BULLET
The projectile expelled from a gun. It is not synonymous with cartridge. Bullets can be of many materials, shapes, weights and constructions such as solid lead, lead with a jacket of harder metal, round-nosed, flat-nosed, hollow-pointed, etc.

CALIBER
The nominal diameter of a projectile of a rifled firearm or the diameter between lands in a rifled barrel. In this country, usually expressed in hundreds of an inch; in Great Britain in thousandths; in Europe and elsewhere in millimeters.

CARBINE
A rifle with a relatively short barrel. Any rifle or carbine with a barrel less than 16" long must be registered with the Bureau of Alcohol, Tobacco and Firearms. Shotguns with barrels less than 18" long fall into the same category.

CARTRIDGE
A single, complete round of ammunition.

CASE, CASING
The envelope (container) of a cartridge. For rifles and handguns it is usually of brass or other metal; for shotguns it is usually of paper or plastic with a metal head and is more often called a "shell."

CENTER-FIRE
A cartridge with its primer located in the center of the base of the case.

CHAMBER
The rear part of the barrel that is formed to accept the cartridge to be fired. A revolver employs a multi-chambered rotating cylinder separated from the stationary barrel.

CHOKE
A constriction at or near the muzzle of a shotgun barrel that affects shot dispersion.

CLIP
A device for holding a group of cartridges. Semantic wars have been fought over the word, with some insisting it is not a synonym for "detachable magazine." For 80 years, however, it has been so used by manufacturers and the military. There is no argument that it can also mean a separate device for holding and transferring a group of cartridges to a fixed or detachable magazine or as a device inserted with cartridges into the mechanism of a firearm becoming, in effect, part of that mechanism.

COP-KILLER BULLET
An inflammatory phrase having neither historical basis nor legal or technical meanings.

CYLINDER
The drum of a revolver that contains the chambers for the ammunition.

DERRINGER
A small single-shot or multi-barreled (rarely more than two) pocket pistol.

DETONATE
To explode with great violence. It is generally associated with high explosives e.g. TNT, dynamite, etc., and not with the relatively slow-burning smokeless gunpowders that are classed as propellants.

DOUBLE-ACTION
A handgun mechanism where pulling the trigger retracts and releases the hammer or firing pin to initiate discharge.

DUM-DUM BULLET
A British military bullet developed in India's Dum-Dum Arsenal and used on India's North West Frontier and in the Sudan in 1897 and 1898. It was a jacketed .303 cal. British bullet with the jacket nose left open to expose the lead core in the hope of increasing effectiveness. Improvement was not pursued, for the Hague Convention of 1899 (not the Geneva Convention of 1925, which dealt largely with gas warfare) outlawed such bullets for warfare. Often "dum-dum" is misused as a term for any soft-nosed or hollow- pointed hunting bullet.

EXPLODING BULLET
A projectile containing an explosive component that acts on contact with the target. Seldom found and generally ineffective as such bullets lack the penetration necessary for defense or hunting.

EXPLOSIVE
Any substance (TNT, etc.) that, through chemical reaction, detonates or violently changes to gas with accompanying heat and pressure. Smokeless powder, by comparison, deflagrates (burns relatively slowly) and depends on its confinement in a gun's cartridge case and chamber for its potential as a propellant to be realized.

FIREARM
A rifle, shotgun or handgun using gunpowder as a propellant. By federal definition, under the 1968 Gun Control Act, antiques are excepted. Under the National Firearms Act, the word designates machine guns, etc. Airguns are not firearms.

FIXED AMMUNITION
A complete cartridge of several obsolete types and of today's rimfire and center-fire versions.

FLASH HIDER/FLASH SUPPRESSOR
A muzzle attachment intended to reduce visible muzzle flash caused by the burning propellant.

GAUGE
The bore size of a shotgun determined by the number of round lead balls of bore diameter that equals a pound.

GUN
The British restrict the term in portable arms to shotguns. Here it is properly used for rifles, shotguns, handguns and airguns, as well as cannon.

GUNPOWDER
Chemical substances of various compositions, particle sizes, shapes and colors that, on ignition, serve as a propellant. Ignited smokeless powder emits minimal quantities of smoke from a gun's muzzle; the older blackpowder emits relatively large quantities of whitish smoke.

HANDGUN
Synonym for pistol.

HIGH-CAPACITY MAGAZINE
An inexact, non-technical term indicating a magazine holding more rounds than might be considered "average."

HOLLOW-POINT BULLET
A bullet with a concavity in its nose to increase expansion on penetration of a solid target.

JACKET
The envelope enclosing the core of a bullet.

LEVER-ACTION
A gun mechanism activated by manual operation of a lever.

MACHINE GUN
A firearm of military significance, often crew-served, that on trigger depression automatically feeds and fires cartridges of rifle size or greater. Civilian ownership in the U.S. has been heavily curtailed and federally regulated since 1934.

MAGAZINE
A spring-loaded container for cartridges that may be an integral part of the gun's mechanism or may be detachable. Detachable magazines for the same gun may be offered by the gun's manufacturer or other manufacturers with various capacities. A gun with a five-shot detachable magazine, for instance, may be fitted with a magazine holding 10, 20, or 50 or more rounds. Box magazines are most commonly located under the receiver with the cartridges stacked vertically. Tube or tubular magazines run through the stock or under the barrel with the cartridges lying horizontally. Drum magazines hold their cartridges in a circular mode. A magazine can also mean a secure storage place for ammunition or explosives.

MAGNUM
A term indicating a relatively heavily loaded metallic cartridge or shotshell and, by extension, a gun safely constructed to fire it.

MULTI-BARRELED
A gun with more than one barrel, the most common being the double-barreled shotgun.

MUSHROOMED BULLET
A description of a bullet whose forward diameter has expanded after penetration.

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

MUZZLE BRAKE
An attachment to or integral part of the barrel intended to trap and divert expanding gasses and reduce recoil.

MUZZLELOADER
The earliest type of gun, now also popular as modern-made replicas, in which blackpowder and projectile(s) are separately loaded in through the muzzle. The term is often applied to cap-and-ball revolvers where the loading is done not actually through the muzzle but through the open ends of the cylinder's chambers.

PELLET GUN
A rifle or pistol using compressed air or CO2 to propel a skirted pellet as opposed to a spherical BB. Not a firearm.

PELLETS
Small spherical projectiles loaded in shotshells and more often called "shot." Also the skirted projectiles used in pellet guns.

PISTOL
Synonymous with "handgun." A gun that is generally held in one hand. It may be of the single-shot, multi-barrel, repeating or semi-automatic variety and includes revolvers.

PISTOL GRIP
The handle of a handgun or protrusion on the buttstock or fore-end of a shoulder-operated gun that resembles the grip or handle of a handgun. A "semi-pistol grip" is one less pronounced than normal; a "vertical pistol grip" is more pronounced than normal.

PLINKING
Informal shooting at any of a variety of inanimate targets. The most often practiced shooting sport in this country.

PRIMER
The ignition component of a cartridge, generally made up of a metallic fulminate or (currently) lead styphnate.

PROPELLANT
In a firearm the chemical composition that is ignited by the primer to generate gas. In air or pellet guns, compressed air or CO2.

PYRODEX
A trade name for a blackpowder substitute, the only such safe substitute known at this time.

RECEIVER
The housing for a firearm's breech (portion of the barrel with chamber into which a cartridge or projectile is loaded) and firing mechanism.

REVOLVER
A gun, usually a handgun, with a multi-chambered cylinder that rotates to successively align each chamber with a single barrel and firing pin.

RIFLE
A shoulder gun with rifled bore.

RIFLING
Spiral grooves in a gun's bore that spin the projectile in flight and impart accuracy. Rifling is present in all true rifles, in most handguns and in some shotgun barrels designed for increasing the accuracy potential of slugs (a slug is a single projectile rather than the more common "shot".)

RIMFIRE
A rimmed or flanged cartridge with the priming mixture located inside the rim of the case. The most famous example is the .22 rimfire. It has been estimated that between 3-4 billion .22 cartridges are loaded in the U.S. each year.

ROUND
Synonym for a cartridge.

SABOT
A lightweight carrier surrounding a heavier projectile of reduced caliber, allowing a firearm to shoot ammunition for which it is not chambered. For example, a hunter could use his .30-30 deer rifle to shoot small game with .22 centerfire bullets.

SATURDAY NIGHT SPECIAL
A catchy phrase having no legal or technical meaning.

SAWED-OFF SHOTGUN (RIFLE)
Common term for federally restricted "short-barreled shotgun (rifle)" i.e. a conventional shotgun with barrel less than 18" (rifle less than 16") or overall length less than 26."

SELECTIVE-FIRE
A firearm's ability to be fired fully automatically, semi-automatically or, in some cases, in burst-fire mode at the option of the firer.

SEMI-AUTOMATIC
A firearm designed to fire a single cartridge, eject the empty case and reload the chamber each time the trigger is pulled.

SHOTGUN
A shoulder gun with smooth-bored barrel(s) primarily intended for firing multiple small, round projectiles, (shot, birdshot, pellets), larger shot (buck shot), single round balls (pumpkin balls) and cylindrical slugs. Some shotgun barrels have rifling to give better accuracy with slugs or greater pattern spread to birdshot.

SHOTSHELL
The cartridge for a shotgun. It is also called a "shell," and its body may be of metal or plastic or of plastic or paper with a metal head. Small shotshells are also made for rifles and handguns and are often used for vermin control.

SILENCER
A virtually prohibited device for attachment to a gun's muzzle for reducing (not silencing) the report. Better terms would be "sound suppressor" or "sound moderator."

SINGLE-SHOT
A gun mechanism lacking a magazine where separately carried ammunition must be manually placed in the gun's chamber for each firing.

SLIDE-ACTION
A gun mechanism activated by manual operation of a horizontally sliding handle almost always located under the barrel. "Pump-action" and "trombone" are synonyms for "slide-action."

SNUB-NOSED
Descriptive of (usually) a revolver with an unusually short barrel.

SUBMACHINE GUN
An automatic firearm commonly firing pistol ammunition intended for close-range combat.

TEFLON
Trade name for a synthetic sometimes used to coat hard bullets to protect the rifling. Other synthetics, nylon for instance, have also been used as bullet coatings. None of these soft coatings has any effect on lethality.

WEAPON
Webster defines it as "an instrument of offensive or defensive combat." Thus an automobile, baseball bat, bottle, chair, firearm, fist, pen knife or shovel is a "weapon," if so used.