Recoil operation
|
|
Recoil operation is one of the firearm actions used in automatic firearms.
It uses the recoil of the barrel to cycle the action.
There is a difference between "blowback" and "breechblock" actions. Recoil operated guns designed for low pressure, low "power" ammunition have "blowback" actions, and recoil operated guns designed for high pressure, high "power" ammunition have "breechblock" actions. The pressure generated by the propellant is so high that it would burst (http://www.thegunzone.com/glock/glock-kb-faq.html) the cartridge case if it was not supported. Normally the sides of the cartridge case are supported by the chamber walls and the head of the cartridge case is supported by the breech. To prevent a ruptured cartridge case, the cartridge case should not be extracted until the pressure acting on the walls of the cartridge case is at a safe level; this means that the bullet has traveled far enough down the barrel so that the pressure has dropped, or the bullet has left the muzzle and the gas has vented out the muzzle.
In lower pressure cartridges, such as 22 Long Rifle, 25 Auto, 32 Auto, or 380 Auto, it is feasable to design a practically useable "blowback" action, in which the barrel is fixed to the frame, and only the mass of the slide and the force of the recoil spring holds the gun closed long enough to support the case and delay extraction until a safe pressure has been achieved. Higher power cartridges, such as 9mm Luger, 40 S&W, or 45 Auto, generate much higher pressure; one could design a blowback action. But the slide would be so heavy as to make the gun difficult to control, or the recoil spring would be so stiff that it would be difficult to manually open the slide. So these guns have breechblock actions.
This is how breechblock action works:
1. The recoil of the bullet going through and leaving the barrel, in the form of gas pressure, drives the breechblock and slide backward.
2. The barrel and the breechblock unlock.
3. Since the spring attaching to the barrel to the frame is firmer than the spring attaching to the slide to the frame, the barrel's cycling back into position is even faster than the slide's cycling, ramming the barrel clear of the breechblock. The extractor, which is a hook on one side of the breechblock, holds the case, pulls it out of the chamber, and the dedicated ejector spring in the breechblock, through the dedicated ejector pin, in the other side of the breechblock, holds the case against the walls of the chamber until the case can fully exit the chamber. The separation of the barrel and the slide opens a slot in the side of the slide that the barrel previously laid under and blocked. The slide flying back ratchets the action into a charged position, ready to strike the next primer.
4. The ejector spring and ejector pin throw an edge of the case forward, and the extractor holds its side of the case until the case spins so that the extractor cannot hold the case, so that the result is the flipping of the case outward. This ejects the spent cartridge's case through the slot in the slide and clears space for the next cartridge.
5. A spring in the magazine pushes all the cartridges up. One cartridge on the top of the pile ends up between the breechblock and the barrel, hooking the new case onto the extractor.
6. And the slide's spring rams the slide, breechblock against and the new cartridge into the barrel, putting the cartridge in the chamber, charging the ejector spring through the ejector pin, and locking the breechblock onto the barrel. The gun is just as it was before, minus one cartridge in the bottom of the magazine, plus heat, noise and the now closed gun recoiling back in the operator's hand(s).
Some of the more common mechanical locks are:
- Tilt locked (Many Browning designs, Sturmgewehr 44)
- Falling-lock locked (Walther P38, Beretta 92FS)
- Rotating bolt (M1 Garand, M1 Carbine, M16, HK G36, AK-74, M1942 Johnson, M2 Mauser)
- Roller locking (MG-42)
- Toggle-locked Luger
- Browning Automatic Shotgun, Femaru STOP pistol.
- Radial Locking (Blaser 93)
There is a further distinction between short-recoil and long recoil operation.
(Short) recoil operation is common in pistols.
The MG-42 machine gun and its descendant the MG-3 use recoil together with roller locking. The Maxim gun and the Barrett M82A1 heavy sniper rifle are also examples of recoil operation.