Machine Gun is a general blanket term that refers to several types of firearms that fire a rapid succession of bullets, shooting projectiles for as long as the operator depresses the trigger, or until the magazine is empty. Submachine guns, assault rifles and heavy machine guns fall under this classification.
The term was introduced in Grand Theft Auto 1 to refer to unspecified firearms which are capable of such firepower, but was eventually retired in Grand Theft Auto III when the range of weapons under the machine gun categorization was expanded, and real-life weapons were introduced for the first time. Since GTA III, specific classifications of machine guns (i.e. Submachine guns, assault rifles, etc.) are more commonly used instead.
GTA 1 — GTA 2
The machine gun name was first seen in GTA 1 for use by a unknown assault rifle-like firearm that is capable of firing larger numbers of bullets within a period of time than a pistol. Because of this trait, the machine gun is far more effective in flooding an area with bullets, increasing the chances for the player to hit targets quicker. However, as the weapon fires a large number of bullets at a time, its ammunition may deplete faster than the player would expect for a pistol. The weapon's rifle design in GTA 1 is also incorporated for use in the game's flamethrower.
Subsequent depictions of the machine gun, in Grand Theft Auto: London 1969, Grand Theft Auto: London 1961 and Grand Theft Auto 2, would undergo several changes in terms of their physical appearance, but generally retains the traits of its predecessor in GTA 1. For both GTA London games, the machine gun is designed without a visible magazine, as it is based on the Sten MkII and the magazine is on the left side of the gun. In GTA 2, the machine gun's damage per bullet was decreased to only half that of the pistol, and is given the appearance of a sub machine gun, being referred to in the game as a S-Uzi Machine Gun, a clear reference to the Uzi name. In addition to a conventional S-Uzi, GTA 2 additionally offers a "Silenced Machine Gun" that features a suppressor intended to muffle the sound of gunfire. In addition, machine guns can be mounted on cars, and the Armed Land Roamer comes with its own form of mounted machine gun. The icon of the gun appears to be an Grease Gun with a shorter barrel and a smaller magazine.
GTA III — present
Beginning GTA III, the machine gun name was retired following the introduction of three different weapons which share traits of a typical machine gun, one sub machine gun (the Uzi) and two assault rifles (the AK-47 and M-16). This resulted in a divergence of weapon groups and a more complex categorization of different types of machine guns.
From Grand Theft Auto: Vice City onwards, there are three classifications of machine guns; sub machine guns (like Uzi's and Micro SMG's), assault rifles (like the M-16 and AK-47), and "true" machine-guns (crew-served weapons like the Browning .30-cal or the M2 Browning .50-cal, which manifests in the series in the form of an M-60 in GTA Vice City. These firearms use a different fire-control group and different internal parts than their semi-automatic equivalents, and different guns may use different systems to cycle the action, such as the delayed-blowback system found in the MP5, or the gas-piston system found in the AK-47. The weapons' primary variance is their firing rate; the faster the cyclic rate, the faster it can send rounds downrange and increase the chance of eliminating enemies, gangs, cops, or even civilians.
Firearms in GTA III and later that fall under the current machine gun categorization include: