A firearm is any type of gun that uses an explosive charge and is designed to be readily carried and used by an individual. The term is legally defined further in different countries.
A machine gun (MG) is a fully automatic, rifled auto-loading firearm designed for sustained direct fire with rifle cartridges. Other automatic firearms such as automatic shotguns and automatic rifles are typically designed more for firing short bursts rather than continuous firepower and are not considered true machine guns. Submachine guns fire handgun cartridges rather than rifle cartridges, therefore they are not considered machine guns, while automatic firearms of 20 mm (0.79 in) caliber or more are classified as autocannons rather than machine guns.
A machine pistol is an autoloading pistol capable of fully automatic fire, including stockless handgun-style submachine guns.
In firearms terminology, an action is the functional mechanism of a breech-loading firearm that handles the ammunition cartridges, or the method by which that mechanism works. Actions are technically not present on muzzleloaders, as all those are single-shot firearms with a closed off breech with the powder and projectile manually loaded from the muzzle. Instead, the muzzleloader ignition mechanism is referred to as the lock.
The MG 34 is a German recoil-operated air-cooled general-purpose machine gun, first tested in 1929, introduced in 1934, and issued to units in 1936. It introduced an entirely new concept in automatic firepower – the Einheitsmaschinengewehr – and is generally considered the world's first general-purpose machine gun (GPMG). Both the MG 34 and MG 42 were erroneously nicknamed "Spandau" by Allied troops, a carryover from the World War I nickname for the MG 08, which was produced at the Spandau Arsenal.
A semi-automatic firearm, also called a self-loading or autoloading firearm, is a repeating firearm whose action mechanism automatically loads a following round of cartridge into the chamber and prepares it for subsequent firing, but requires the shooter to manually actuate the trigger in order to discharge each shot. Typically, this involves the weapon's action utilizing the excess energy released during the preceding shot to unlock and move the bolt, extracting and ejecting the spent cartridge case from the chamber, re-cocking the firing mechanism, and loading a new cartridge into the firing chamber, all without input from the user. To fire again, however, the user must actively release the trigger, allow it to "reset", before pulling the trigger again to fire off the next round. As a result, each trigger pull only discharges a single round from a semi-automatic weapon, as opposed to a fully automatic weapon, which will shoot continuously as long as the ammunition is replete and the trigger is kept depressed.
A semi-automatic pistol is a handgun that automatically ejects and loads cartridges in its chamber after every shot fired. Only one round of ammunition is fired each time the trigger is pulled, as the pistol's fire control group disconnects the trigger mechanism from the firing pin/striker until the trigger has been released and reset.
A repeating rifle is a single-barreled rifle capable of repeated discharges between each ammunition reload. This is typically achieved by having multiple cartridges stored in a magazine and then fed individually into the chamber by a reciprocating bolt, via either a manual or automatic action mechanism, while the act of chambering the round typically also recocks the hammer/striker for the following shot. In common usage, the term "repeating rifle" most often refers specifically to manual repeating rifles, as opposed to self-loading rifles, which use the recoil, gas, or blowback of the previous shot to cycle the action and load the next round, even though all self-loading firearms are technically a subcategory of repeating firearms.
Selective fire, or select fire, is the capability of a weapon to be adjusted to fire in semi-automatic, fully automatic, and/or burst mode. The modes are chosen by means of a selector switch, which varies depending on the weapon's design. Some selective-fire weapons have burst fire mechanisms to limit the maximum number of shots fired automatically in this mode. The most common limits are two or three rounds per trigger pull. Fully automatic fire refers to the ability for a weapon to fire continuously until either the feeding mechanism is emptied or the trigger is released. Semi-automatic refers to the ability to fire one round per trigger pull.
A magazine, often simply called a mag, is an ammunition storage and feeding device for a repeating firearm, either integral within the gun or externally attached. The magazine functions by holding several cartridges within itself and sequentially pushing each one into a position where it may be readily loaded into the barrel chamber by the firearm's moving action. The detachable magazine is sometimes colloquially referred to as a "clip", although this is technically inaccurate since a clip is actually an accessory device used to help load ammunition into a magazine or cylinder.
Pump action is a type of manual firearm action that is operated by moving a sliding handguard on the gun's forestock. When shooting, the sliding forend is pulled rearward to eject any expended cartridge and typically to cock the hammer or striker, and then pushed forward to load a new cartridge into the chamber. Most pump-action firearms use an integral tubular magazine, although some do use detachable box magazines. Pump-action firearms are typically associated with shotguns, although it has been used in rifles, grenade launchers, as well as other types of firearms. A firearm using this operating mechanism is colloquially referred to as a pumpgun.
A firearm is said to fire from an open bolt or open breech if, when ready to fire, the bolt and working parts are held to the rear of the receiver, with no round in the chamber. When the trigger is actuated, the bolt travels forward, feeds a cartridge from the magazine or belt into the chamber, and fires that cartridge in the same movement. Like any other self-loading design, the action is cycled by the energy released from the propellant, which sends the bolt back to the rear, compressing the mainspring in readiness for firing the next round. In an open-bolt gun firing semi-automatically, the bolt is caught and held at this point by the sear after each shot; and in automatic open-bolt fire, it's caught and held in this manner whenever the trigger is released. In contrast to this, in closed-bolt guns, the trigger and sear do not affect the movement of the bolt directly.
Blowback is a system of operation for self-loading firearms that obtains energy from the motion of the cartridge case as it is pushed to the rear by expanding gas created by the ignition of the propellant charge.
Rate of fire is the frequency at which a specific weapon can fire or launch its projectiles. This can be influenced by several factors, including operator training level, mechanical limitations, ammunition availability, and weapon condition. In modern weaponry, it is usually measured in rounds per minute or rounds per second.
A self-loading rifle or autoloading rifle is a rifle with an action using a portion of the energy of each cartridge fired to load another cartridge. Self-loading pistols are similar, but intended to be held and fired by a single hand, while rifles are designed to be held with both hands and fired from the shoulder.
A trigger is a mechanism that actuates the function of a ranged weapon such as a firearm, airgun, crossbow, or speargun. The word may also be used to describe a switch that initiates the operation of other non-shooting devices such as a trap, a power tool, or a quick release. A small amount of energy applied to the trigger leads to the release of much more energy.
In automatic firearms, burst mode or burst-fire is a firing mode enabling the shooter to fire a predetermined number of rounds, usually two or three rounds on hand held weapons to fifty or more rounds on autocannons, with a single pull of the trigger. This firing mode is commonly used in submachine guns and assault rifles. Other types of firearms, such as machine pistols, including the Heckler & Koch VP70 and Beretta 93R also have a burst mode.
The following are terms related to firearms and ammunition topics.
Self-loading firearm is a repeating firearm that can use some of the excess energy released from propellant combustion to cycle its action and facilitate loading of subsequent rounds of ammunition into the chamber, without needing the user to do any extra loading work with his hands.
A repeating firearm or repeater is any firearm that is capable of being fired repeatedly before having to be manually reloaded with new ammunition into the firearm.
