Monday, August 6, 2007

How machine guns work

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Here is a collection of some very cool and descriptive flash animations that shows the different types of techniques machine guns uses. All the animations are taken form HowStuffWorks website.

Before taking on machine guns, lets begin with the old standard double-action revolver.

Revolvers




Click on the trigger to see how a revolver fires.


This gun has a revolving cylinder, with six breeches for six cartridges. When you pull the trigger on a revolver, several things happen:

1. Initially, the trigger lever pushes the hammer backward.
As it moves backward, the hammer compresses a metal spring in the gun stock (the handle).
At the same time, the trigger rotates the cylinder so the next breech chamber is positioned in front of the gun barrel.

2. When you pull the trigger all the way back, the lever releases the hammer.
3. The compressed spring drives the hammer forward.
4. The hammer slams into the primer at the back of the cartridge, igniting the primer.
5. The primer sets off the propellent.

The exploding propellent drives the bullet out of the gun at high speed.
The inside of the barrel has a spiral groove cut into it, which serves to spin the bullet as it exits the gun. This gives the bullet better stability as it flies through the air, increasing accuracy.

When the propellant explodes, the cartridge case expands. The case temporarily seals the breech, so all the expanding gas pushes forward rather than backward.

Machine Guns: Recoil Systems

The first automatic machine guns had a recoil-based system. In 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. For simplicity's sake, this animation doesn't show the cartridge loading, extraction and ejection mechanisms.


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. 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 bolt is connected to an extractor, which removes the spent shell from the barrel. 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.

Machine Guns: Blowback System

A blowback system is something like a recoil system, except the barrel is fixed in the gun housing and the barrel and bolt do not lock together. You can see how this mechanism works in the diagram below.




Click and hold the trigger to see how a blowback-action gun fires. For simplicity's sake, this animation doesn't show the cartridge loading, extraction and ejection mechanisms.


This gun has a sliding bolt (3) held in place by a spring, a spring-driven cartridge magazine (5), and a trigger mechanism (1). When you slide the bolt back, the trigger sear (2) holds it in place. When you pull the trigger, the sear releases the bolt, and the spring drives it forward. After the bolt chambers the cartridge, the firing pin sets off the primer, which ignites the propellant.

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 lines up in front of the bolt 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.

Machine Guns: Gas System

The gas system is similar to the blowback system, but it has some additional pieces. The main addition is a narrow piston, attached to the bolt, that slides back and forth in a cylinder positioned above the gun barrel. You can see how this system works in the diagram below.




Click and hold the trigger to see how a gas-action gun fires. For simplicity's sake, this animation doesn't show the cartridge loading, extraction and ejection mechanisms.


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 above 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.

Machine Gun Feeding: Belt System

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. You can see how this sort of mechanism works in the diagram below.




Top-view diagram of a common feed mechanism.


The bolt (1) in this gun has a small cam roller (5) on top of it. As the bolt moves, the cam roller slides back and forth in a long, grooved feed cam piece (2). When the cam roller slides forward, it pushes the feed cam to the right against a return spring (6). When the cam roller slides backward, the spring pushes the cam back to the left. As it moves, the feed cam pivots a feed cam lever from side to side. The feed cam lever is attached to a spring-loaded pawl (8), a curved gripper that rests on top of the ammunition belt. As the cam and lever move, the pawl moves out, grabs onto a cartridge and pulls the belt through the gun. When the bolt moves forward, it pushes the next cartridge into the chamber. You can see how this works in the diagram below.




Click and hold the trigger to see
how the loading and ejection system works.


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.

For more information visit:
HowStuffWorks: Machine guns
The PKM General Purpose Machine Gun
Infoplease: small arms overview

3 comments:

  1. I have been wondering how a machine gun works!

    it was very helpful. You should do a diagram of a sks rifle

    ReplyDelete
  2. awesome one! just brilliant and it really helps small students studying in schools to think more! hope you explains pretty much more!

    ReplyDelete
  3. Good God, I thought it was rocket science tech but it's plain levers pushing and pulling.

    ReplyDelete

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