Glossary of Firearms Related Terms

Action

The “action” of a firearm describes how a spent round is ejected from the gun and how the next round is loaded in. This is also know as “cycling the gun”. Types of actions are described below.

Single Action Revolver
Single Action Revolver is one that requires the operator to manually cock (or pull the hammer back) on the firearm in order to chamber the next round and prepare the gun to be fired. These single action guns are often depicted in western movies where you see a gunfighter use one hand to slam back the hammer and the other to pull the trigger.

Double Action Revolver
Unlike the single action, with a double action each time the trigger is pulled the cylinder rotates a fresh round into the firing chamber, cocks the hammer back and then releases the hammer to fire the round. These types of revolvers can be fired nearly as quickly as semi automatic handguns.

Lever Action
Typically seen on rifles, a lever is located under the stock and behind the trigger. The lever is pulled out and then pushed back up against the stock. The first motion – pulling the lever out – expels the spent cartridge. The second motion – pushing the lever back in – loads the next round into the firing chamber.

Bolt Action
Also more typically found on rifles, a bolt action utilizes a sliding metal cylindar (or bolt) to the rear of the gun just behind the firing chamber. The bolt has a handle that extends out to the right or left of the gun. The operator would pull the bolt back to eject a spent round and then push it forward again to load the next round into the chamber.

Pump Action
Similar to Bolt Action, a pump action firearm – usually a shotgun – uses an internal mechanism to cycle the weapon. In this case, though, the mechanism is in front of the firing chamber and connects to a handle on the outside of the weapon. This handle, usually under the barrel, is pulled back to expel hte spent round and pushed forward to load the next round.

Semi-Automatic Action
A semi-automatic firearm is one whereby the empty bullet casing is ejected and a new round is loaded into the firing chamber automatically. This is made possible by capturing some of the gases released at the time the cartridge is fired and using those gases to expel the spent case and a chamber the next round.

Fully Automatic Action
Like the semi-automatic action, the fully automatic action uses the gases from the spent round to manuver internal mechanics to cycle a round through the gun. In this case, however, the weapon allows for the trigger to be held down to enabling mutliple rounds be fired rather than a single round with each trigger pull.

AR

Contrary to popular belief, “AR” doest NOT stand for “Automatic Rifle” or “Assault Rifle”. The “AR” actually comes from the name of the company that first mass produced a rifle known as the AR15. The company’s name is Armalite. The development of the original AR15 was lead by one of the greatest firearms designers of the 20th century, Eugene Stoner. Today, the term “AR” really refers to any Modern Sporting Rifle (MSR) and military rifle which is based on the original AR15 design.

Assault Rifle

The term “assault rifle” is not a technical designation for any specific firearm but rather a political term used to describe semi-automatic rifles that resemble military rifles. In strict military terms, an assault rifle refers to any lightweight rifle that can fire in “select fire” mode. This means any combination of semi-automatic fire, burst fire or fully automatic fire. By definition, any rifle that can fire in fully automatic mode is also considered a “machine gun” which is illegal to own by civilians in the United States.

Automatic

The term “automatic firearm”, or sometimes just “automatic” really is a misnomer and is often misused. What are often refered to as automatic pistols such as the Glock 19 or the Beretta 92 are actually semi-automatic firearms. This means they fire one bullet each time the trigger is pulled (see above for the definition of semi-automatic). People often refer to a pistol as an automatic simply to differntiate it from a revolver. Revolvers were the most common type of handgun used by civilians and law enforcement ever since they became widely availble in the late 19th century. When semi-automatic pistols became more widely manufactured and available to the public in the late 1970s and 1980s, it was then that they began being referred to as “automatics” in contrast to the double-action revolvers they began to replace.

Blowback

Blowback refers to a semiautomatic pistol action in which the top (or “slide”) of the pistol is forced backwards by the gases expelled when a bullet cartridge is fired. The blowback motion ejects the spent round and loads the next round into the firing chamber.

Breach

Put simply, the breach is the back of a firearm. More specifically the back portion of the gun where the firing chamber is located.

Breach-loading Firearm

Nearly all modern firearms and just about any firearm manufactured since the mid-19th century is a breach loading-loading firearm. This simply means that the round is loaded into the gun near the rear of the firearm rather than dropped down the muzzle (or front) of the gun the way muskets and similar single-shot firearms were loaded in the centuries before the bullet cartridge was invented.

Bullpup

In traditional firearms, the action (see above) is typically located close to the trigger of the weapon – specifically right above it. This was done due to simple mechanics – the closer the trigger is to the action, fewer moving parts are needed. In a bullpup design – as seen in weapons like the P90 submachine gun and the Tavor rifle from IWI – the action is in the rear of the gun, behind the trigger. This design, while technically more challenging, provides two advantages over traditional firearm design: (1) with the action essentially in stock of the rifle, the barrel can be as long as a traditional rifle while the overall length of the weapon is shorter; (2) the action being closer to the operator’s body lessons the recoil of the weapon.

Bursts or “Burst Mode”

Burst firing is a type of automatic firing mode whereby multiple rounds are fired with a single pull of the trigger. This is commonly found only in military rifles as in most countries civilians are not allowed to own automatic firearms or they have to get special licensing to own automatics. One of the most historically relevant firearms to fire in burst mode was the U.S. M16 assault rifle which fired in three-round bursts. This feature is available in more modern military rifles today.

Caliber

Caliber refers to the size of a bullet and also the barrel of a gun. Specifically, caliber refers to the diameter of the bullet or the inside of the barrel. Read more about bullet caliber and bullet sizes here.

Cycle or Cycling

The action of expelling spent bullet cartridges (or casings) from a firearm and subsequently loading a fresh round into the firing chamber is know as cycling.

Hunting Rifles

A rifle referred to as a hunting rifle is used primarily for hunting game and has a number of common characteristics including, but not limited to the following:

• A long, rifled barrel – typically longer than 16″
• Is fired from the shoulder
• Contains an internal magazine (although some do have detachable magazines but this is not common)
• Most are bolt action although some are semi-automatic
• A telescopic site can be mounted to the top to improve accuracy over distance

Machine Guns

Machine Guns are any style of firearm that can fire in fully automatic mode meaning that the weapon will continue to fire as long as the trigger is held down and there is ammunition being fed into the chamber. Machine guns were outlawed for civilian use in the United States under the National Firearms Act of 1934. In the United States, only civilians possessing a Class 3 firearms permit can own a fully automatic weapon.

Modern Sporting Rifle (MSR)

Modern sporting rifles are typically used for casual target shooting and competitve shooting as well as hunting. MSRs are different from hunting rifles mainly because they possess common features that are not normally found on typical hunting rifles. These include, but are not limited to the following:

• Short to mid-sized, rifled barrel – most commonly 12″ to 20″
• A pistol grip to aid in comfort, accuracy and maneuverability
• A detachable magazine capable of holding anywhere from 5 rounds up to 100 rounds of ammunition (although legality of large capacity magazines varies by state)
• Attachments can be added in various forms including such items as electronic sites, foregrips, flashlights, laser pointers and others
• Most MSRs have interchangeable parts that can be replaced or upgraded including firing pins, bolt carrier groups, butt stocks, handguards and more

Muzzle

The front, open end of a gun.

Muzzle-loading Firearm

A firearm that is loaded from the front of the gun. Traditionally, this was done by first pouring gunpowder down the barrel followed by some kind of paper wadding and finally the bullet itself. While there are modern muzzle-loading firearms being manufactured for sale in the United States, the development of repeating firearms in the 19th centure made muzzle-loaders mostly obsolete.

Repeating Firearm

A repeating firearm can be fired more than once without the need to load a fresh round into the gun. This includes revolvers as well as any type of gun that uses either a removable or internal magazine that stores the ammunition until it is loaded into the firing chamber through some type of action.

Rifle

A rifle is any long barreled gun in which the barrel has spiraling grooves cut into it causing the bullet to rotate 360 degrees before exiting the muzzle of the gun. The rotation causes the fired round to rotate while in flight – much like a spiraling football – creating greater accuracy over longer distances.

Rifling

The spiraling grooves cut into a gun barrel that cause the bullet to spin providing greater accuracy.

Selective Fire

Firearms with selective fire are able to fire rounds of ammunition in multiple ways. Most commonly, selective fire weapons can be changed from single shot (or semi-automatic) to fully automatic. Some weapons can select burst mode in addition to or in place of full auto mode.

Semi-automatic

A firearm described as semi-automatic can fire a single round each time the trigger is pulled. This is not the same as full auto (described above). What the “automatic” part of a semi-auto firearm is describing is specifically the action – in this case the action is automatic – meaning that the empty bullet casing is ejected and a new round is loaded into the firing chamber automatically each time the trigger is pulled. This is made possible by capturing some of the gases released at the time the cartridge is fired and using those gases to expel the spent case and chamber the next round. The video to the right shows how a semi-automatic pistol operates.