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Sturgeon's House

Why are most modern rifles Gas-Operated?


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This may have already been answered, but why are so many modern assault rifles gas-operated, when blowback-operated designs are (generally speaking) simpler/cheaper to manufacture and require less maintenance? I've been doing some research and can't seem to figure out why for the life of me. Any assistance is greatly appreciated.

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23 hours ago, CharlieAlphaVictor said:

This may have already been answered, but why are so many modern assault rifles gas-operated, when blowback-operated designs are (generally speaking) simpler/cheaper to manufacture and require less maintenance? I've been doing some research and can't seem to figure out why for the life of me. Any assistance is greatly appreciated.

 

Straight blowback is unsuitable for high pressure rifle cartridges. You can use delayed blowback or retarded blowback for rifle calibers, but they are not cheaper than a well-designed modern gas-operated gun. For example, when HK was in trouble after the collapse of East Germany and the cancellation of the G11, they did not revive the retarded blowback HK33/41 family to produce the new weapon for the cash-strapped Bundeswehr, they created an all-new gas operated gun in the G36. And it was indeed cheaper.

This raises the question, if retarded blowback isn't necessarily cheaper than gas operation, why did anyone use it at all? And how did the G3 come very close to out-competing the FAL, despite being available a few years later. There's really two parts to the answer. First, retarded blowback is one of several methods tried to solve several problems that early gas operated rifles had, foremost of which is that they didn't handle pressure variances well. The solution to these myriad problems turned out to simply be refinement of the gas operated mechanism, best embodied by the M16 and the AK families. Both of these include robust, corrosion-proof materials and the M16 also fired noncorrosive ammunition, which completely solved the issues of erosion around the gas port causing the rifle to become more gassed over time. Both also include refinements to the mechanism which make them less sensitive to pressure variances in general (the AK is just designed to be overgassed in the first place, making excessive port pressure less of an issue, and includes generous underslide which helps reduce wear and tear on the bolt, and M16's DI system provides similar benefits). Retarded blowback guns, in theory, avoid all of these problems by simply not having a gas system in the first place, which in 1945 seemed like a very intuitive solution to the Germans who couldn't afford corrosion resistant materials. The famous HK roller locked family of guns are all derived from these efforts. The gas pressure problem is also why so many rifles from the late 1940s and 1950s have gas regulators, as often this was a very tidy solution to both that problem and also to give the gun better ability to fire early rifle grenades.

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Well the FAMAS isn't a bad design. Given that they were going to make their own production line from the ground up, I wouldn't say that it's an irrationally expensive design either. On the modern US commercial firearms market there has been some efforts to make semi-locked or locked bolts for pistol caliber carbines and submachineguns. This lowers felt recoil, ameliorates performance with suppressors and with some larger pistol calibers. SIG has a gas operated, rotating bolt design, but I wouldn't say that it's completely clear that the SIG design is leaps and bounds better than the CMMG radial delayed blowback.

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If you look at the difference in manufacturing costs, I think Sturgeon does have a good point. The tubing or operating rods or whatever needed for the gas system are rarely very expensive parts. I'd guess that the difference in costs associated to the bolt head and barrel extension is larger than the entire cost of small parts for the gas system. I could be wrong.

Also, there's the development hurdle of designing a new rifle. If you're trying to invent a roller delayed blowback, as far as I understand, you'd have to experiment with different angles on pieces that are made from hardened steel. I might be overestimating the amount of work to do that, but my spontaneous estimation is that that would be way more time consuming than modifying an SVT-40 (AR-18) gas system by moving the gas port up and down the barrel and changing its size. All you really need to do that is a serious drill and a way to plug your old hole...

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4 hours ago, Miroslav said:

Well the FAMAS isn't a bad design. Given that they were going to make their own production line from the ground up, I wouldn't say that it's an irrationally expensive design either. On the modern US commercial firearms market there has been some efforts to make semi-locked or locked bolts for pistol caliber carbines and submachineguns. This lowers felt recoil, ameliorates performance with suppressors and with some larger pistol calibers. SIG has a gas operated, rotating bolt design, but I wouldn't say that it's completely clear that the SIG design is leaps and bounds better than the CMMG radial delayed blowback.

 

The FAMAS design goes back to the 1960s, and it does have some problems by the standards of modern assault rifles. But I agree that it's a sound design overall.

Retarded blowback is a good idea for pistol caliber carbines, but I'm not sure pistol caliber carbines themselves are the most compelling things. Submachineguns  have applications (like SCW) but besides that...

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3 hours ago, Miroslav said:

If you look at the difference in manufacturing costs, I think Sturgeon does have a good point. The tubing or operating rods or whatever needed for the gas system are rarely very expensive parts. I'd guess that the difference in costs associated to the bolt head and barrel extension is larger than the entire cost of small parts for the gas system. I could be wrong.

Also, there's the development hurdle of designing a new rifle. If you're trying to invent a roller delayed blowback, as far as I understand, you'd have to experiment with different angles on pieces that are made from hardened steel. I might be overestimating the amount of work to do that, but my spontaneous estimation is that that would be way more time consuming than modifying an SVT-40 (AR-18) gas system by moving the gas port up and down the barrel and changing its size. All you really need to do that is a serious drill and a way to plug your old hole...


And for a modern rifle like an AR-15, the bolt and extension are trivial to make in relative terms. Certainly, it's no harder to make an AR bolt than it is to make the bolt assembly for a G3.

Gas operated guns really are easy to tune versus retarded blowback guns, certainly. Although you can theoretically tune retarded blowback guns via math alone, in practice there are always adjustments, which in the case of something like a G3 would involve the production of quite a few steuerstucks.

And what's the benefit? You get a gun that's no cheaper, probably more expensive in fact, not any more compact or lighter, and which is more sensitive to different kinds of ammunition. Oh, and it's more violent.

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