Glossary on Firearms Terminology

CCBP books, 2002-2019

By Matt Conner, UC Davis Librarian, with thanks to Fred Bach for his assistance

Following is a glossary of firearms terminology commonly used in discussions of gun violence.  The definitions are generally accepted in the shooting community except for areas of emerging or conflicted usage and controversy that are acknowledged.  These terms will be further explained and set into their historical context in a talk by the author on Thursday, October 3, 2019, 5:30 – 6:30 pm in Shields Library Room 167.  A short list of annotated references follows to supplement the glossary and to provide additional reading.

This glossary is intended as a community resource. We value your input in making this a comprehensive resource for all. If you would like to suggest a term to add, or to suggest an edit or correction, please contact the Campus Community Book Project at 

Action – The central mechanism of a firearm, generally applied to rifles.  It consists of the receiver, a short hollow tube of metal with cutouts to accept the other functional parts of the weapon.  These include the barrel, for directing the bullet; the magazine, for feeding rounds into the chamber; the trigger, for firing the gun; the buttstock for shouldering and controlling the weapon; and the bolt for locking the action during discharge.  One cycle of the action consists of locking the bolt on a cartridge, firing the cartridge, retracting the bolt to eject the spent case, and closing the bolt to feed a new cartridge.  Actions are classified by the different means of operating the bolt:  lever-action, bolt-action, falling-block, semiauto and automatic.

AR-15 – Commonly called “America’s rifle” by gun enthusiasts.  This is the civilian version of the standard rifle of the American military since the Vietnam War.  It is identical in most respects to the military version except that it lacks the capacity for automatic fire.  It is thus at the center of debates about assault rifles and gun control.  The letter designation does not stand for Assault Rifle but for Armalite, the name of the company that produced the original design for the military.  The rifle is commonly sold in its military caliber of .223/5.56X45mm but is also offered in the larger .308/7.62X51mm.  

Assault rifle – A cross between a carbine (a short rifle firing a pistol caliber cartridge) and a “full-power” battle rifle.  It is based on an historical weapon developed by Nazi Germany in WWII called the Sturmgewehr (Stg.) 44, and its name in translation (assault rifle) has been adopted for this category of weapon.  There is widespread agreement that assault rifles are those weapons that resemble this original, especially in terms of the six “evil features” (See Evil Features).  In essence, the type is a shortened semiautomatic rifle firing an intermediate powered cartridge with a large detachable magazine.  The controversy surrounds the precise dividing line between assault rifles and other kinds of rifles based on the feature of automatic fire (See Automatic).  Different opinions reference different definitions of an assault rifle to support their case.

Automatic – A firearm which fires continuously while the trigger is depressed like a machine gun or submachine gun.

Barrel – A steel tube through which a bullet travels after discharge in the action.  The tube compresses gases from the ignition of gunpowder to propel the bullet and guide it to its target.

Bore – The inside face of the barrel which contacts the bullet during its travel.

Bullet – The projectile fired by a gun.  Modern bullets are conical masses of lead, jacketed in copper and designed for aerodynamic flight.  They generally weigh a few grams each.

Bullet button – A device to disqualify a gun as an assault rifle by removing one of the six “evil features” of the Assault Weapon Ban (AWB) 1994-2004 (See Evil Features), the detachable magazine.  The definition of a detachable magazine is one that can be inserted and removed by hand.  The bullet button is a device that must be engaged to insert the magazine that cannot be operated by hand.  It requires a simple tool such as a bullet to depress.  While satisfying the requirements of the AWB, the bullet button, with its ease of use, has been regarded as a legal loophole for assault rifles, and the device is currently banned in California.

Bump fire – A means of manipulating semiautomatic weapons to achieve continual fire while keeping the trigger depressed.

Bump stock – A device to facilitate the process of bump firing wherein a semiautomatic gun is manipulated so as to simulate automatic fire.  Bump stocks are buttstocks (See Stock) with a spring which exerts a tension on the action so that continual firing can be achieved by depressing the trigger.  Bump stocks were banned by the Trump administration.  However, they have generated controversy about definitions and enforcement since proponents claim that one can bump fire without the stock and that the stock does not permit automatic fire in a technical sense.

Caliber – A measure of the size of a bullet.  It corresponds to the largest diameter of its cross-section and is commonly measured in inches or millimeters.  The metric version also has a measure for the length of the case for additional information on the power of a cartridge, e.g. 8X57mm means a bullet width of 8mm and a case length of 57mm.  The greater the case length, the greater the power.  Common calibers in discussions of gun violence include the following.  Handgun:  9x19mm (the most widespread handgun cartridge in the world), .40, .45.  Rifle:  .223, 5.56X45mm; .308, 7.62X51mm.

Carbine – Shortened rifle, firing a pistol cartridge.

Cartridge – Package of gunpowder and a bullet that can be conveniently inserted into a firearm for firing.  The cartridge consists of (in order of operation):  primer (shock sensitive explosive), gunpowder (ignites to propel the bullet), case (cylindrically shaped brass container to hold the gunpowder), and bullet.  A metal rod called a firing pin strikes the primer to generate a spark which ignites the gunpowder to propel the bullet.

Case – Cylindrical brass container for holding the gunpowder and bullet.  It is closed at one end (the case head) which holds the primer and open at the other (case mouth) for seating the bullet.  After the bullet is discharged, the empty case is pulled backward by the retracting bolt and ejected from the gun, making space for a new cartridge to be loaded.

Centerfire – Refers to the placement of the primer on the case head.  A primer in the form of a small disk at the center of the case head distinguishes a centerfire cartridge.  This placement allows more powerful cartridges than previous designs and is sometimes used synonymously with “high-power.”

Chamber – The end of the barrel that meets the receiver and which holds the bullet when it is ready to be discharged.

Clip – A metal rack that holds cartridges together to permit them to be loaded together instead of one at a time.  Clips generally come in sizes of five or eight cartridges.

Evil Features – A colloquial term used for the six defining features of an assault rifle in the AWB that are intended to differentiate a military firearm from one for sporting or other purposes.  Assault rifles are defined as having a detachable magazine and any two of the other features.

  1. Flash hider – A device that conceals the flash from the muzzle at discharge and helps to hide the shooter.
  2. Bayonet lug – A device for attaching a bayonet to the rifle.
  3. Grenade launcher attachment – Rails for mounting a grenade launcher.
  4. Detachable magazine – A magazine that can be detached from the weapon and allows rapid reloading of cartridges.
  5. Pistol Grip – A grip that extends down from a standard rifle buttstock and resembles the grip of a handgun.  It is designed to provide greater control during rapid fire shooting.
  6. Folding/telescoping stock – Replaces the standard rifle buttstock with a metal one, hinged to the gun, so that it can be swung 180 degrees forward to become flush with the gun.  Modern variants telescope to reduce their length.  This device was pioneered by airborne troops to take up less space during transport and generally makes the weapon smaller and more concealable. 

Full Metal Jacket – A bullet design popularized as the title of a Stanley Kubrick movie about the Vietnam War (1987).  (See Bullet.)  These bullets, in deference to the Geneva Convention, completely enclose the lead portion with a copper jacket to prevent expansion or fragmentation that causes additional damage.  Thus, full metal jacket bullets, contrary to the movie usage, are the most “benign” type of bullet.

Gas operation – A system which uses the gases from gunpowder to cycle the action.  Gas from a discharge is bled off from the barrel near the muzzle where it is routed back through the forestock (See Stock) to push back the bolt and cycle the action.

Glock – A brand of handgun of revolutionary design that has taken military and law enforcement by storm and appears often in crime.  Its innovations consist of a largely plastic construction that is virtually indestructible, extreme reliability of function, and simplicity of operation.  In particular, its safety (See Safety) is built into the trigger pull.  As a result, Glocks are carried locked and loaded (See Locked and Loaded) and can be fired by simply pulling the trigger.  This has resulted in numbers of accidents.

Handgun – A gun small enough to be operated with one hand.  The category is divided into revolvers, with multiple chambers per barrel, and pistols with one chamber per barrel.  Handguns generally use separate calibers from rifles with comparable bullet sizes having much reduced powder capacities for short range use.

High capacity magazine – The term is relative to the definition of “standard” which is not fixed.  Hunting laws limit magazine capacity to three to five cartridges.  Adopting this as a standard, “high capacity” has been used legally to refer to magazines with capacity greater than 10.

High power – An ill-defined term with at least two distinct usages.  The older usage was for rifle calibers of .30 or greater used by standard military rifles of WWII and before.  But this term can also refer to any centerfire cartridge whose design allows it to handle much greater pressures than rimfire calibers.  Thus a .223 centerfire rifle cartridge is vastly more powerful than a .22 rimfire although their bullet width is virtually the same.  Centerfire projectiles move in the range of 2400 feet per second or about 1600 miles per hour.

Locked and Loaded – Refers to locking the bolt closed on a round that is loaded into the chamber.  It generally means “ready to fire.”

Longarm – A rifle size firearm designed to be hoisted to the shoulder.  Much of the length and weight comes from the long barrels.  Standard lengths are 26 inches to 18 inches.

Modern sporting rifle – A term used for weapons which have all the features of assault rifles without automatic fire.  The term implicitly contrasts with an alleged “military” definition of assault rifles that specifies an automatic capacity, although this definition has not been documented.  The term further suggests that the action of modern sporting rifles is no different from those legal for hunting and that a military classification of these weapons is based on superficial, cosmetic features rather than reality.  This term is used almost exclusively for AR-15 style rifles.

Military weapon – Ill-defined term that attempts to distinguish between weapons used specifically for military purposes and those for other uses such as sport or self-defense.  Military usage is associated with extreme firepower and ammunition capacity as well as appearance.  The term is generally applied in the discussion about assault rifles as well as to certain modifications for handguns, such as extended magazines (projecting below the grip of the gun).  One criticism of this term is that just about every firearm has had military use at some point.

Magazine – A metal container for holding cartridges for rapid reloading.  It differs from a clip in that it also contains a means for advancing the cartridges.  A common design is a rectangular “box” magazine with cartridges stacked in a single column or a staggered double column with a spring underneath them.  After a cartridge is fired and the case extracted, the spring (“follower”) pushes the next cartridge up to be stripped off by the advancing bolt and pushed into the chamber.  Larger magazines take the shape of drums containing cartridges lined up in concentric layers under spring pressure.  Magazines are differentiated as external (detachable) and internal where they are fixed to the receiver of the gun.  Detachable magazines can be much larger and permit much faster reloading, and they are one of the evil features defining assault rifles under the AWB.  This feature is generally considered the most important of the six and subject to the most scrutiny.

Pistol – A handgun with one chamber per barrel.  A common design is a semiautomatic pistol fed by a magazine located in the grip.

Pistol brace – A brace similar to a crutch design in which stabilizing metal bands surround the user’s arms.  Such bands are used to replace a conventional buttstock to allow a user to fire a rifle with one hand rather than two; this is feasible for a drastically shortened rifles.  Pistol braces are sometimes seen as loopholes for rifles that are shortened below the legal limit of 14 inches.  Such weapons are classified as pistols while retaining the power of rifles.

“Poison bullet” – A bullet design to produce maximum damage through tumbling and/or fragmentation.  This is done by creating an empty space inside the bullet with a movable mass behind it.  When the bullet impacts, the mass is thrown forward, changing the projectile’s center of mass and causing it to tumble.  The name was created for the 5.45X39mm ammunition used by the Soviet Union in Afghanistan; this is the Russian counterpart to the 5.56X45mm ammunition used by American AR type rifles.  The Afghan rebels (Mujahideen, now Taliban) found that this relatively small caliber would cause outsize damage wherever it struck, destroying limbs and heads.  However, the principle is not new and was used in the .303/7.7X56mm ammunition used for the British Enfield series of rifles in the first half of the 20th century.  This ammunition skirts the Geneva Convention, which prohibits exploding or expanding bullets, since the “Poison bullet” design achieves its effects through instability while remaining, largely, intact.  The “Poison bullet” achieves the same instability that the 5.56X45mm ammunition sought to gain by mating light bullets with high velocity.

Repeater – A gun with a magazine that can hold more than one cartridge at a time.

Revolver – Used almost exclusively for handguns, this action contains a rotating cylinder that holds multiple cartridges (typically six).   Each cycle of the action turns the cylinder to line up a fresh cartridge with the barrel.

Rifling – Spiral grooves running down the length of the bore which engrave the bullet as it travels, imparting spin which stabilizes it in flight to increase range and accuracy.

Rimfire – An older design for ammunition in which the primer is distributed around a rim, protruding outwardly around the case head (See Case).  This design is restricted to the lower pressures of earlier blackpowder ammunition in use before the invention of modern smokeless powder in the 1890s.  Other than historical ammunition, rimfire is relegated now to .22 rimfire.  This is the traditional “.22” of popular reference whose most common variant is .22 Long Rifle (LR).  It propels bullets at velocities less than 1000 feet per second, or subsonic.

Round – Synonymous with cartridge.  Its likely etymology is a reference to repetition (as in boxing round) or, possibly, ammunition for cannons consisting of metal balls.

Safety – A switch on a gun which renders it inoperative by blocking the trigger mechanism.

Semiauto – Actions which fire one shot with each pull of the trigger.  Most semiauto rifles use a gas piston.  Most semiauto pistols use recoil operation in which part of the gun is fixed and another part can move under recoil along a track so that the relative motion operates the action.  Semiautomatic pistols are often called “automatics,” as a shorthand use, which leads to confusion.  For example, the (arguably) most well-known pistol cartridge of all, used for the U.S. military’s sidearm for most of the 20th century, is the .45 ACP where the acronym stands for Automatic Colt Pistol.  

Side-arm – Synonym for a handgun.

Single-shot/action – An action without a magazine that can only load one cartridge at a time directly into the chamber.  Single-action can also refer to handguns with magazines in which the trigger has one action (releasing a cocked hammer) rather than two (cocking and releasing the hammer) known as “double-action.”  The distinction has implications for safety and the weight of the trigger pull.

Stock – An accessory of rifles that consists of two parts, the forestock and the buttstock.  The forestock surrounds the barrel, allowing it to be gripped and stabilized by the non-trigger hand.  The buttstock is a trapezoidal section of material attached to the rear of the action which allows the weapon to be braced against the shoulder for stability and aligned with the eye for aiming.  Stocks were traditionally made of wood but have also been made of synthetic materials in recent decades.

Telescopic sight (scope) – A telescope, with markings (reticle), such as a crosshair, that mounts over the barrel of a gun and extends its accuracy to much greater ranges.  The scope housing encloses mechanisms for changing the orientation of the lens to line the reticle up with the impact point of the bullet at various distances.


A Gun Lingo Glossary for Those Unfamiliar with Firearms
Online glossary of firearms terminology.

Glossary of Firearms Terms
Another online glossary.

When Lawmakers Try to Ban Assault Rifes, Gunmakers Adapt
Excellent interactive graphic on the defining features of an assault rifle.

Browning, J., & Gentry, C. (1964). John M. Browning, American Gunmaker; a illustrated biography of the man and his guns. Garden City, NY: Doubleday.
Biography of the foremost inventor of modern firearms who created virtually all the technology in use today.

Popenker, M. R., & Williams, A. G. (2004). Assault Rifle. Ramsbury, UK: Crowood Press.
Source on assault rifles.

Sajer, Guy (1971).  The Forgotten Soldier.  New York:  Harper & Row. 
The definitive memoir of the Eastern Front of WWII told from the perspective of a German soldier including his own experience of using the first assault rifle.