A machine gun is a fully automatic mounted or portable firearm, usually designed to fire bullets in quick succession from an ammunition belt or magazine, typically at a rate of three to eighteen hundred rounds per minute.
Fully automatic weapons are generally categorized as submachine guns, machine guns, or autocannons. Submachine guns are hand-held automatic weapons for personal defense or short-range combat firing pistol-caliber rounds. A machine gun is often portable to a certain degree, but is generally used when attached to a mount or fired from the ground on a bipod or tripod, and generally fires a rifle cartridge and is capable of sustained fire. Light machine guns are small enough to be fired hand-held, but are more effective when fired from a prone position. The difference between machine guns and autocannons is based on caliber, with autocannons using calibers larger than 16 mm.,and whether the gun fires conventional bullets or explosive rounds. Guns firing large-caliber explosive rounds are generally considered either autocannons or automatic grenade launchers ("grenade machine guns"). In contrast to submachine guns and autocannons, machine guns (like rifles) tend to have a very high ratio of barrel length to caliber (a long barrel for a small caliber); indeed, a true machine gun is essentially a fully automatic rifle, and often the primary criterion for a machine gun as opposed to an automatic rifle is the presence of a quick-change barrel or other cooling system. Automatic rifles and (more commonly) assault rifles may be capable of fully automatic fire, but are not designed for sustained fire.
In United States gun law, machine gun is a technical term for any fully automatic firearm, and also for any component or part that will modify an existing firearm such that it functions as a fully automatic firearm.
It would not be until the mid-19th century that successful machine-gun designs came into existence. The key characteristic of modern machine guns, their relatively high rate of fire and more importantly machine (automatic) loading, came with the Model 1862 Gatling gun, which was adopted by the United States Navy. These weapons were still powered by hand; however, this changed with Hiram Maxim's idea of harnessing recoil energy to power reloading in his Maxim machine gun. Dr. Gatling also experimented with electric-motor-powered models; this externally powered machine reloading has seen use in modern weapons as well. The Vandenburg and Miltrailleuse volley (organ) gun concepts have been revived partially in the early 21st century in the form of electronically controlled, multibarreled volley guns. It is important to note that what exactly constitutes a machine gun, and whether volley guns are a type of machine gun, and to what extent some earlier types of devices are considered to be like machine guns, is a matter of debate in many cases and can vary depending which language and exact definition is used.
Early rapid-firing weapons
The first known ancestors of multi-shot weapons were early revolvers made in Europe in the late 1500s. One is a shoulder-gun-length weapon made in Nuremberg, Germany, circa 1580. Another is a revolving arquebus, produced by Hans Stopler of Nuremberg in 1597.
Another large, early repeating was created by James Puckle, a London lawyer, who patented what he called "The Puckle Gun" on May 15, 1718. It was a design for a 1 in. (25.4 mm) caliber, flintlock revolver cannon able to fire 9 rounds before reloading, intended for use on ships.According to Puckle, it was able to fire round bullets at Christians and square bullets at Turks.While ahead of its time, foreshadowing the designs of revolvers, it was not adopted or produced.
In 1777, Philadelphia gunsmith Joseph Belton offered the Continental Congress a "new improved gun", which was capable of firing up to twenty shots in five seconds, automatically, and was capable of being loaded by a cartridge. Congress requested that Belton modify 100 flintlock muskets to fire eight shots in this manner, but rescinded the order when Belton's price proved too high.
In the early and mid-19th century, a number of rapid-firing weapons appeared which offered multi-shot fire, and a number of semi-automatic weapons as well as volley guns. Volley guns (such as the Mitrailleuse) and double barreled pistols relied on duplicating all parts of the gun. Pepperbox pistols did away with needing multiple hammers but used multiple barrels. Revolvers further reduced this to only needing a pre-prepared magazine using the same barrel and ignitions. However, like the Puckle gun, they were still only semiautomatic.
The Agar Gun, otherwise known as a "coffee-mill gun" because of its resemblance to a coffee mill, was invented by Wilson Agar at the beginning of the US Civil War. The weapon featured automatic loading through ammunition being loaded in a hopper above the weapon. The weapon featured a single barrel and fired through the turning of a hand crank. The weapon was demonstrated to President Lincoln in 1861. He was so impressed with the weapon that he purchased 10 on the spot for $1,500 apiece. The Union Army eventually purchased a total of 54 of the weapons. However, due to antiquated views of the Ordnance Department the weapons, like its more famous counterpart the Gatling Gun, saw only limited use.
The Gatling gun, patented in 1861 by Richard Jordan Gatling, was the first to offer controlled, sequential fire with automatic loading. The design's key features were machine loading of prepared cartridges and a hand-operated crank for sequential high-speed firing. It first saw very limited action in the American Civil War; it was subsequently improved and used in the Franco-Prussian war and North-West Rebellion. Many were sold to other armies in the late 19th century and continued to be used into the early 20th century, until they were gradually supplanted by Maxim guns. Early multi-barrel guns were approximately the size and weight of contemporary artillery pieces, and were often perceived as a replacement for cannon firing grapeshot or canister shot.The large wheels required to move these guns around required a high firing position which increased the vulnerability of their crews.Sustained firing of gunpowder cartridges generated a cloud of smoke making concealment impossible until smokeless powder became available in the late 19th century.Gatling guns were targeted by artillery they could not reach and their crews were targeted by snipers they could not see.The Gatling gun was used most successfully to expand European colonial empires by killing warriors of non-industrialized societies.
Gatlings were the first widely used rapid-fire guns and, due to their multiple barrels, could offer more sustained fire than the first generation of air-cooled, recoil-operated machine guns. The weight, complexity, and resulting cost of the multibarrel design meant recoil-operated weapons, which could be made lighter and cheaper, would supplant them. Recoil-operated machine guns were light enough to be moved by one man, were easier to move through rough terrain, and could be fired from a lower, protected position. It would be another 50 years before the concept was again used to allow extremely high rates of fire, such as in miniguns, and automatic aircraft cannon.
The first self-powered machine gun was invented in 1884 by Sir Hiram Maxim. The "Maxim gun" used the recoil power of the previously fired bullet to reload rather than being hand-powered, enabling a much higher rate of fire than was possible using earlier designs such as the Nordenfelt and Gatling weapons. Maxim also introduced the use of water cooling, via a water jacket around the barrel, to reduce overheating. Maxim's gun was widely adopted and derivative designs were used on all sides during the First World War. The design required fewer crew and was lighter and more usable than the Nordenfelt and Gatling guns. First World War combat experience greatly increased the importance of the machine gun. The United States Army issued four machine guns per regiment in 1912, but that allowance increased to 336 machine guns per regiment by 1919.
Heavy guns based on the Maxim such as the Vickers machine gun were joined by many other machine weapons, which mostly had their start in the early 20th century such as the Hotchkiss machine gun. Submachine guns (e.g., the German MP18) as well as lighter machine guns (the Chauchat, for example) saw their first major use in World War I, along with heavy use of large-caliber machine guns. The biggest single cause of casualties in World War I was actually artillery, but combined with wire entanglements, machine guns earned a fearsome reputation. The automatic mechanisms of machine guns were applied to handguns, giving rise to automatic pistols (and eventually machine pistols) such as the Borchardt (1890s) and later submachine guns (such as the Beretta 1918). Machine guns were mounted in aircraft for the first time in World War I. Firing through a moving propeller was solved in a variety of ways, including the interrupter gear, metal reinforcement of the propeller, or simply avoiding the problem with wing-mounted guns or having a pusher propeller.
Interwar era and World War II
During the interwar years, many new designs were developed, such as the Browning M2 and the Thompson sub-machine gun, which, along with others, were used in World War II. The trend toward automatic rifles, light machine guns, and more powerful sub-machine guns resulted in a wide variety of firearms that combined characteristics of ordinary rifles and machine guns. The Cei-Rigotti (20th century), Fedorov Avtomat (1910s), AVS-36 Simonov (1930s), MP44, M2 Carbine, AK-47, and M16 have come to be known as assault rifles (after the German term sturmgewehr). Many aircraft were equipped with machine cannon, and similar cannon (nicknamed "Pom-pom guns") were used as antiaircraft weapons. The designs of Bofors of Sweden and Oerlikon of Switzerland were widely used by both sides and have greatly influenced similar weapons developed since then.
Germany developed during the interwar years the first widely used and successful general-purpose machine gun, the Maschinengewehr 34. The Maschinengewehr 42 was developed from it and was much cheaper to produce. The current GPMG of the German Army, the MG3, is a direct evolution of the MG42. Many other modern machine guns, including the US M60 and the FN MAG borrow elements of the design of the MG42.
The most common interface on machine guns is a pistol grip and trigger. On earlier manual machine guns, the most common type was a hand crank. On externally powered machine guns, such as miniguns, an electronic button or trigger on a joystick is commonly used. Light machine guns often have a butt stock attached, while vehicle and tripod mounted machine guns usually have spade grips. In the late 20th century, scopes and other complex optics became more common as opposed to the more basic iron sights.
Loading systems in early manual machine guns were often from a hopper of loose (un-linked) cartridges. Manual-operated volley guns usually had to be reloaded manually all at once (each barrel reloaded by hand). With hoppers, the rounds could often be added while the weapon was firing. This gradually changed to belt-fed types. Belts were either held in the open by the person, or in a bag or box. Some modern vehicle machine guns used linkless feed systems however.
Modern machine guns are commonly mounted in one of four ways. The first is a bipod – often these are integrated with the weapon. This is common on light machine guns and some medium machine guns. Another is a tripod, where the person holding it does not form a 'leg' of support. Medium and heavy machine guns usually use tripods. On ships and aircraft machine guns are usually mounted on a pintle mount – basically a steel post that is connected to the frame. Tripod and pintle mounts are usually used with spade grips. The last major mounting type is one that is disconnected from humans, as part of an armament system, such as a tank coaxial or part of aircraft's armament. These are usually electrically fired and have complex sighting systems. For examples of this, see US Helicopter Armament Subsystems.