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Posted: 11/9/2005 8:24:07 PM EDT
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What are the limitations of gas-retarded blowback technology -- that is, how much pressure, how large a cartridge, etc? I have a P7M8 and have found the action to be amazingly reliable. It also permits a very low bore line and a fixed barrel, which makes it easy to shoot and accurate. Is it possible to design a weapon around this operating principle for a slightly larger cartridge (e.g., FN5.7 or 30 M-1) and operate it at 50kpsi or thereabouts? Rampant speculation is fine, so please offer your thoughts/opinions. |
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my crude understanding of blowback technology: secret to blowback technology is to not have the bolt blow back before the bullet leaves the barrel otherwise you get a bunch of gas in the chamber end of the gun which isn't good. You'll have to continue to use heavier and heavier bolts to achieve this when using heavier and heavier loads. So now you a big heavy ass bolt flying back, which makes the gun heavy btw, which in turn will have to slam forward again to chamber the next round. If you want a lighter bolt but still want blow back you have to delay the blowback, with rollers like in your HK pistol, or find a way to keep the barrel and bolt (or slide) together until the bullet leaves the barrel. In a pistol, the slide can be considered the "bolt". Berettas use a locking block, 1911's have a barrel linkage pin to the slide and so on. Then there's other ways to move the bolt/slide back with gas, gas operated guns like the AR15 feed gas directly to the bolt carrier, other systems slap a piston to do the same like the M1 carbine. The I guess there's other ways to move the bolt back, that's mechanically with an outside power source like on chain guns which use an electric motor. |
I have a P7, a PPKS, and a G3. The two pistols operate on chamber pressure vs spring pressure and slide inertia. The G3, being chambered for 7.62x51 has the locking roller design to keep the breech shut until the pressure drops low enough to allow safe operation. A pistol chambered for a rifle powered cartridge would be a very very heavy design.
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| somebody please correct me if i am wrong but given a large enough spring isn't a blowback design possible for every cartridge? in pistols it seems that blowback is common with .380acp and smaller and there are a few in 9x19. but the storm in .45acp is blowback but it has a larger spring. |
It is not only a question of the spring, but also the mass of the sprung, moving part, and its inertia. |
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HK got around some of the problem with high-pressure blowbacks in the VP-70. They used extra deep rifling that allowed some gas to blow by which reduced pressure, and muzzle velocity. Yes, a .45 blowback can be made. The M3 Greasegun is one right there, the Marlin camp carbine another. It's just physics. The Germans experimented with a gas retared rifle at the end of WWII. It used the STG-44 round. There's no reason you can't use it for other intermeadiate cartridges. |
Pretty much. The Russians had a grenade launcher that pre dates our MK19 by about 20 years that was a blowback action. According to test reports it kicked like a mule.
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