Encyclopedia  |   World Factbook  |   World Flags  |   Reference Tables  |   List of Lists     
   Academic Disciplines  |   Historical Timeline  |   Themed Timelines  |   Biographies  |   How-Tos     
Sponsor by The Tattoo Collection
Machine gun
Main Page | See live article | Alphabetical index

Machine gun

A machine gun is a "fully automatic" projectile weapon that is capable of firing bullets in rapid succession. Unlike Semi-automatic firearms, which require one trigger pull per bullet fired, a machine gun will continue to fire bullets as long as the trigger is held down. Although the term "machine gun" is often used to describe all fully automatic weapons, a distinction can be made based on the size of the bullet used. A machine gun with a bullet caliber of more than 12.7mm (0.5 inch) is called an automatic cannon while smaller caliber guns would still be called "machine guns".

The machine gun's primary role in ground-combat is to provide suppressing fire on an opposing force's position. This forces the enemy to take cover. This either halts an opposing offensive, or allows friendly forces to move onto the field with less danger.

To this end, most light machine guns are not designed for repeatability of aim or accuracy. Most are designed with a small degree of inaccuracy, to lay down a field of fire. This is referred to as the "cone" of fire, because the rounds spread out as they travel. Light machine guns usually have simple iron sights. A newer intuitive aiming system, favored by the Israelis is to alternate solid and tracer rounds, so shooters can walk the fire into the target, and direct other soldiers' fire. Even newer are laser sights that are used by police and anti-terrorist services.

Assault rifles are a compromise between the light machine gun and the traditional soldier's rifle, allowing single-shot, burst and (sometimes) full-automatic fire options. See that article for more details.

Many heavy machine guns, such as the M2 0.50 Cal machine guns are so accurate that they can actually be used to snipe targets at great distances. Some models have been equipped with aim points that can be preset.

Table of contents
1 Components
2 Operation
3 History
4 See also
5 External Links

Components

All machine guns require the following components:
  1. A feed system to load the firing chamber. Cartridges can be fed into the chamber using a variety of means. The most common are a spring fed magazine or an ammunition belt.
  2. A trigger mechanism to fire the round. This includes the actual trigger, a trigger sear to catch the bolt, a bolt and a firing pin, as well as other components. Typically, the act of pulling the trigger causes something to strike the primer on the round in the chamber, and disengages the sears. This allows continual cycling of the bolt until the trigger is released. A sear then grabs the bolt or firing pin. This stops the machine gun at some point in its cycle.
  3. An extractor system to eject the spent or misfired cartridge. Usually this is fairly simple. A pin on the side of the bolt catches a ridge on the cartridge and flicks it out an ejection port.

These components form a mechanism which must be powered by something. If powered by a spring absorbing the recoil of a fired cartridge, it is called
recoil-operated. If powered by the expanding gasses of a fired cartridge, it is called gas-actuated. If it powered by an external force, such as a motor, it is called a chain gun.

Operation

All machine guns follow a cycle: A mechanism makes the firing pin fire the cartridge, activating the ejection and reloading steps. The cycle repeats. This full cycle takes a fraction of a second, and can thus occur many times per second. The operation is basically the same, regardless of the means of activating these mechanisms. Some examples:

Heavy machine guns have interchangeable barrels. During use these must be changed periodically to avoid overheating. The higher the rate of fire, the more often barrels must be changed and allowed to cool. To minimize this, most such guns are usually not fired continually for long periods of time, or at the highest rate of fire.

Not all machine guns strike the primer in the same way. In blowback machine guns, the act of seating the round also fires the round. In gas operated and recoil-operated guns, a separate step in the firing sequence is needed to strike the round. In progressive-fire guns, the firing pin is cycled by cams.

In weapons where the round seats and fires at the same time, mechanical timing is essential for operator safety, to prevent the round from firing before it is seated properly. This is especially important in weapons like the 40mm grenade launcher, where high explosives are present in the rounds being fired.

Machine guns are controlled by one or more mechanical sears. When a sear is in place, it effectively stops the bolt at some point in its range of motion. Some sears stop the bolt when it is locked to the rear. Other sears stop the firing pin from going forward after the round is locked into the chamber.

Almost all weapons have a "safety" sear, which simply keeps the trigger from engaging.

History

Multi-shot guns have a long development stretching back to some of the earliest firearms, but a single device with a high-rate of fire beyond several shots saw its first known attempt in the 1700s, but it would not be till the mid-1800s that successful designs of this type came about. Effective multi-shot small arms, the ancestors of single action revolvers, came earlier. For example, Giuseppe Fieschi used a multishot firearm in an attempt to assassinate King Louis Philippe of France in 1838. (see Firearms) The most prominent characteristic of modern machine guns would come with the Gatling gun, their high rate of fire. The key design feature of modern machine guns would have to wait till Hiram Maxim, and his idea of using recoil energy to reload in the Maxim machine gun, as opposed to being hand powered.

The first known ancestor of machine weapons 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. (25.4mm) caliber flintlock machine 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 (whom he evidently felt deserved a more painful death). While ahead of its time, foreshadowing the designs of revolvers and machine cannons, it was not adopted or produced.

In the mid-19th century, a number of rapid-firing weapons appeared which formed the last evolutionary steps to a true machine gun. The French Mitrailleuse of the 1860s was a multi-barrelled weapon (technically a volley gun), consisting of up to 37 rifled barrels arranged in a cylinder and mounted similarly to an ordinary cannon. Although put to use in the Franco-Prussian War of 1870, it was poorly deployed and its flaws rendered it a largely useless weapon in the field.

The Gatling gun was closer to the machine gun template; patented in 1861 by Richard Jordan Gatling, the design's key feature was machine loading of cartridges and a hand operated crank for sequential high-speed firing. Its hand-driven firing meant that it was not a true automatic weapon, so technically it does not qualify as a machine gun. It first saw very limited action in the American Civil War and was subsequently sold to many other armies during the 1870s and 1880s. Apart from some use by the French in the Franco-Prussian War, it did not see much action due to its expense and weight. Nonetheless, where used it was effective in warfare. The Gatling principle was reused over a century later in the chain gun design.

The first true machine gun was the Maxim machine gun, invented in 1883 by Hiram Maxim. It used the recoil energy 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. Maxim's other great innovation was the use of water cooling (via a water jacket around the barrel) to reduce overheating. Maxim's gun sparked a cascade of new designs and was widely adopted. The design required less crew, was lighter, and more useable than earlier Gatling guns.

Heavy guns such as the Vickers machine gun were joined by many other machine weapons, which mostly had their start in the early 20th century. Submachine guns (e.g. the Thompson submachine gun, or 'Tommy gun') as well as lighter machine guns (the BAR for example) saw their first major use in WW1 along with heavy use of large-caliber machine guns. Design features of machine guns were applied to automatic handguns, "machine pistols", such as the Luger (although these did not yet have full automatic fire). 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.

During the inter-war years, many new designs were developed, such as the Browning 50-caliber, in 1933, which, along with the others were used in World War II. The trend toward automatic rifles, lighter machine guns, and more powerful submachine guns culminated in the invention of Germany's revolutionary MP44 assault rifle, a weapon that combined characteristics of an ordinary rifle and a machine gun. Many aircraft were equipped with machine cannons, and similar cannon (nicknamed "pom-pom guns") were used as anti-aircraft weapons. The designs of Bofors of Sweden were widely used by both sides and have greatly influenced similar weapons developed since then.

The Cold War era saw mostly a refinement of weapon types in the form of lower weight and higher reliability. Aircraft saw more use of automatic cannons and widespread use of various machine guns on helicopters. Some new subtypes and kinds of machine guns arose as well, such as even larger heavy machine guns and even lighter submachine guns and automatic pistols. The use of water-cooled machine guns decreased in favor of air-cooled types. Chain guns were devised to provide heavy anti-vehicle and anti-aircraft weapons.

In the 21st century, advances in armor rendered lower power guns less effective, especially submachine guns. Replacements with higher penetration (FN P90) were created, but adoption has been slow. The development of conventional machine guns has been slowed by the fact that existing designs of machine guns are adequate for most purposes, although significant developments are taking place with regard to anti-armour and anti-missile weapons.

In the future, electronically controlled machine guns with ultra-high rates of fire may see use in some applications. The trend towards higher reliability and lower mass for a given power will likely continue.

See also

External Links


''Machine Gun is also the name of a free jazz album by Peter Brötzmann as well as the New York based improvising band Machine Gun which featured Thomas Chapin and Sonny Sharrock.