Fully Automatic
The Gatling gun is often considered a machine gun because it shoots a large number of bullets in a short amount of time. But unlike modern machine guns, it is not fully automatic. You have to keep cranking if you want to keep shooting. The first fully automatic machine gun is credited to an American named Hiram Maxim. Maxim's remarkable gun could shoot more than 500 rounds per minute, giving it the firepower of about 100 rifles.
Hiram Maxim and one of his early machine gun designs: When Maxim introduced his weapon to the British army in 1885, he changed the battlefield forever.
The basic idea behind Maxim's gun, as well as the hundreds of machine gun designs that followed, was to use the power of the cartridge explosion to reload and re-cock the gun after each shot. There are three basic mechanisms for harnessing this power:
Recoil systems
Blowback systems
Gas mechanisms
The first automatic machine guns had a recoil-based system. In nature, every action has an equal and opposite reaction. This principle is responsible for the recoil effect in guns. When you propel a bullet down the barrel, the forward force of the bullet has an opposite force that pushes the gun backward.
In a gun built like a revolver, this recoil force just pushes the gun back at the shooter. But in a recoil-based machine gun, moving mechanisms inside the gun absorb some of this recoil force. You can see how this works in the diagram below.
Click and hold the trigger to see how a recoil-action gun fires.
Here's the process: To prepare this gun to fire, you pull the breech bolt (1) back, so it pushes in the rear spring (2). The trigger sear (3) catches onto the bolt and holds it in place. The feed system runs an ammunition belt through the gun, loading a cartridge into the breech (more on this later). When you pull the trigger, it releases the bolt, and the spring drives the bolt forward. The bolt pushes the cartridge from the breech into the chamber. The impact of the bolt firing pin on the cartridge ignites the primer, which explodes the propellant, which drives the bullet down the barrel.
The barrel and the bolt have a locking mechanism that fastens them together on impact. In this gun, both the bolt and the barrel can move freely in the gun housing. The force of the moving bullet applies an opposite force on the barrel, pushing it and the bolt backward. As the bolt and barrel slide backward, they move past a metal piece that unlocks them. When the pieces separate, the barrel spring (4) pushes the barrel forward, while the bolt keeps moving backward.
The bolt is connected to an extractor, which removes the spent shell from the barrel. There are a number of extractor systems in modern guns, but the basic idea in all of them is fairly simple. In a typical system, the extractor has a small lip that grips onto a narrow rim at the base of the shell. As the bolt recoils, the extractor slides with it, pulling the empty shell backward.
The backward motion of the bolt also activates the ejection system. The ejector's job is to remove the spent shell from the extractor and drive it out of an ejection port (more on this later).
When the spent shell is extracted, the feeding system can load a new cartridge into the breech. If you keep the trigger depressed, the rear spring will drive the bolt against the new cartridge, starting the whole cycle over again. If you release the trigger, the sear will catch hold of the bolt and keep it from swinging forward.
The explosive gas from the cartridge drives the bullet down the barrel. At the same time, the gas pressure pushes in the opposite direction, forcing the bolt backward. As in the recoil system, an extractor pulls the shell out of the barrel, and the ejector forces it out of the gun. A new cartridge enters the chamber just before the spring pushes the bolt forward, starting the process all over again. This continues as long as you hold the trigger down and there is ammunition feeding into the system.
A U.S. Marine, fighting in Okinawa, Japan, during World War II, fires a military-issue Thompson's submachine gun. The Thompson's, commonly known as the "Tommy gun," was a popular weapon with both soldiers and gangsters in the 1930s and '40s.
The gas system is similar to the blowback system, but it has some additional pieces. The main addition is a narrow piston, which slides back and forth in a cylinder positioned underneath the gun barrel and connects to the bolt.
This gun is basically the same as a blowback-system gun, but the rear force of the explosion doesn't propel the bolt backward. Instead, the forward gas pressure pushes the bolt back. When the bolt swings forward to fire a cartridge, it locks onto the barrel. Once the bullet makes its way down the barrel, the expanding gasses can bleed off into the cylinder underneath the barrel. This gas pressure pushes the piston backward, moving it along the bottom of the bolt. The sliding piston first unlocks the bolt from the barrel, and then pushes the bolt back so a new cartridge can enter the breech.
These diagrams only depict particular examples of how these systems work. There are hundreds and hundreds of machine gun models in existence, each with its own specific firing mechanism. These guns differ in a number of other ways as well. In the next section, we'll look at some of the key differences between various machine gun models.
Feeding and Size
One of the main differences between different machine gun models is the loading mechanism. One popular system is the spring-operated magazine. In this system, a spring pushes cartridges in a magazine casing up into the breech. The main advantages of this mechanism are that it is reliable, lightweight and easy to use. The main disadvantage is that it can only hold a relatively small amount of ammunition.
A similar system is the ammunition hopper, such as the one used in a Gatling gun. Hoppers are just metal boxes that fit on top of the machine gun mechanism. One by one, the cartridges fall out of the hopper and into the breech. Hoppers can hold a good amount of ammunition, and they're easy to reload, but they are fairly cumbersome and only work if the gun is positioned right side up.
For sheer volume of ammunition, the belt system is usually the best option. Ammunition belts consist of a long string of cartridges fastened together with pieces of canvas or, more often, attached by small metal links. Guns that use this sort of ammo have a feed mechanism driven by the recoil motion of the bolt.
The feed system drives the ammunition belt through cartridge guides (2) just above the breech. As the bolt slides forward, the top of it pushes on the next cartridge in line. This drives the cartridge out of the belt, against the chambering ramp (3). The chambering ramp forces the cartridge down in front of the bolt. The bolt has a small extractor, which grips the base of the cartridge shell when the cartridge slides into place. As the cartridge slides in front of the bolt, it depresses the spring-loaded ejector (6).
When the firing pin hits the primer, propelling the bullet down the barrel, the explosive force drives the operating rod and attached bolt backward. The extractor pulls the spent shell out of the breech. As the bolt keeps moving backward, the spring-loaded ejector pushes on the base of the shell. When the shell clears the chamber wall, the ejector springs forward, popping the shell out of the gun through the ejection port.
This system lets you fire continuously without reloading. Theoretically, you could make ammunition belts of any length, so they are a great means of providing a constant supply of ammunition. The problem is that the belt is fairly cumbersome, and there's a relatively high likelihood of the feed mechanism jamming.
The Vickers MK1 belt-fed machine gun, a favorite of the British military, played a crucial role in World War I and World War II. The gun is cooled with a special water-filled jacket. As the water boils, the steam flows out to a collection can, where it condenses back into a liquid for re-use.
Heavy belt-fed machine guns, usually mounted on a tripod or a vehicle, may need more than one operator. Individual troops usually carry light weapons, with extendible bipods or tripods for stability. Smaller automatic guns that use cartridge magazines are classified as automatic rifles, assault rifles or submachine guns. In a general sense, the term "machine gun" describes all automatic weapons, including these smaller weapons, but it also used to describe heavy belt-fed guns specifically.
Gun manufacturers are continually adding new modifications to machine guns, but the basic mechanism has remained the same for more than a hundred years. Whether or not you've ever held a machine gun, or even seen one, this device has had a profound effect on your life. Machine guns have had a hand in dissolving nations, repressing revolutions, overthrowing governments and ending wars. In no uncertain terms, the machine gun is one of the most important military developments in the history of man.
