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Blowback guns
#1
Okay so friend and I were talking and he was telling me that the mini-14s are a blowback design. I was under the assumption that most semi-auto firearms operated on a blowback style operation. So am I thinking correctly or is there a difference between blowback and gas piston guns.
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#2
They are gas piston guns.
arjohnson, proud to be a member of pa2a.org since Sep 2012.
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#3
arjohnson;42063 Wrote:They are gas piston guns.
assuming you mean the mini-14s.
The main thing though I am curious about though. Is there a difference between a gas piston gun and a blowback gun?
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#4
The Hobbit;42064 Wrote:
arjohnson;42063 Wrote:They are gas piston guns.
assuming you mean the mini-14s.
The main thing though I am curious about though. Is there a difference between a gas piston gun and a blowback gun?

Gas systems cycle the action from gas being pushed as the bullet passes the gas port in the barrel.

Blowback gets energy from the motion of the cartridge case as it is pushed to the rear by expanding gases created by the ignition of the propellant charge.
arjohnson, proud to be a member of pa2a.org since Sep 2012.
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#5
arjohnson;42066 Wrote:
The Hobbit;42064 Wrote:assuming you mean the mini-14s.
The main thing though I am curious about though. Is there a difference between a gas piston gun and a blowback gun?

Gas systems cycle the action from gas being pushed as the bullet passes the gas port in the barrel.

Blowback gets energy from the motion of the cartridge case as it is pushed to the rear by expanding gases created by the ignition of the propellant charge.
thanks was not sure if there was a difference.
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#6
The term blowback operated generally refers to pistols or submachine guns that have nothing locking the bolt or slide to the barrel. The only thing keeping the bolt or slide closed long enough for pressure to drop is the recoil spring and the weight of the slide/bolt.

With pistols, blowback operation is generally limited to calibers in the .380acp/9x18mm Makarov class and lower. The Hi Points being an exception. With the smaller calibers, it's generally just a stiff recoil spring holding the breech closed long enough for the chamber pressure to drop to a safe level. With the Hi Points in 9mm, .40 S&W and .45acp, the recoil spring and the weight of the oversized slide keep the breech closed.

With submachine guns, like the later Thompsons, the Grease Guns and even Uzis, it's a heavy bolt that has to be moved by the recoil of each round. With the open bolt guns, the momentum of that heavy bolt going forward increases the delay just a bit more.

Not all submachine guns work that way though. The MP5 and basically all of the non AR based HKs are what's called semi retarded blow back. They don't use a gas piston or even direct impingement. They use the recoil of the round like the blowback pistols. But, they have a pair of rollers on the bolt. When the round is fired, it forces the rollers into cutouts in the receiver. Once the chamber pressure drops, the rollers retract into the bolt to let it continue it's way to the rear to extract the spent casing. The CZ52 pistol uses the same system.

Most rifles use either a tipping bolt locking system like the SKS and FAL or a rotating bolt system like the AR, AK and Garand. They can be either gas piston driven like the AK or direct impingement like the AR.

The M1 Carbine uses a modifed Williams Floating Chamber. There is a small piston at the gas port that basically slaps the action to the rear. It only moves a fraction of an inch. The Remington 550 and the Colt Ace .22 conversion for the 1911 use the original floating chamber design.

Tune in next week when I go over the differences between long stroke and short stroke gas piston systems Smile
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