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Old October 31, 2012, 10:23 PM   #1
barnbwt
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Air Cushion Recoil Spring?

Has anyone (successfully) made a semi/full auto that uses a captured air chamber behind the bolt to spring the action back into battery? I have my doubts as to the potential reliablity (seals, mainly) of such a system, but it seems like it would work very well if it worked at all, and be very consistent. Moreover, it'd be extremely light weight and compact. If an internal spring on the bolt/carrier could tension the locking elements of the element into their seats at the "in battery" position, no latent pressure on the rear of the bolt/carrier would be needed, right?

TCB
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Old October 31, 2012, 10:47 PM   #2
the rifleer
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I've never heard of anything like that, but what I think would work much better is have a piston in a cylinder (like an engine) behind the bolt. Then you still get compression but eliminate any reliability issues from rubber seals breaking.

This might actually work


The down fall I see is it would have to be kept lubricated (again, like an engine) or else it would wear out, but that should take tens of thousands of cycles. I bet it would work, but would be higher maintenance than a traditional spring and not have any real advantage. If you are licensed to do it, have the tools and the time, why not?
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Old October 31, 2012, 11:48 PM   #3
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Olympic Arms use to make a pneumatic recoil buffer for the AR15... eliminated the recoil spring and buffer. I built a rifle for a guy about 6-7 years ago and fit one... he loved it. Some loved 'em, some had problems. I'm not even sure they make them anymore.



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Old November 1, 2012, 09:29 AM   #4
stubbicatt
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Rather than a constant rate of compression as one would have in a simple coil spring one would have a rising rate of compression with the pneumatic system. Bolt opening for the first inch or so would be linear, but the last little bit would take quite a bit more effort/force to accomplish.

That's the downside as I see it.
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Old November 1, 2012, 08:08 PM   #5
barnbwt
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Quote:
Rather than a constant rate of compression as one would have in a simple coil spring one would have a rising rate of compression with the pneumatic system. Bolt opening for the first inch or so would be linear, but the last little bit would take quite a bit more effort/force to accomplish.
True, you'd definitely need either a heavy bolt for blowback, or a positive breech lock via op-rod/carrier until the air cushion would deliver enough force to arrest the bolt. My thought was also that barrel gas could even be used to pre-pressurize the chamber resisting the bolt so that more force is immediately available when the bolt unlocks.

Sorta kinda like the HK P7 pistol, only the chamber gasses would be used to cycle the action as opposed to holding the bolt in battery (which the P7 doesn't even do; it basically functions like a blow-back).

The non-linearity (PV=RT, right? It's been a while since college...) of the force/deflection might actually be a good thing; you could deliver the force of a large, heavy spring in a short piston, if you can get the pressures up high enough. There are also two-stage recoil springs out there that basically function the same way; initially linear, then more steeply linear as the second spring is compressed. It's something that could be designed around, is what I'm trying to say

I'm convinced someone has tried this at some point in the past (hell, they tried triangular bullets, this is sane by comparison ), so I'll do some more digging. Most likely I'll find it didn't work due to leaky/sticky seals or dirt sensitivity. With enough pressure, the pistons don't really need to seal all that well, though (think how loose op-rod pistons are). I'll bet the real trick is getting a round to chamber properly when the bolt is flying forward with chamber gas behind it. Imagine if your AK/AR/whatever chambered brass as violently as it is extracted

This needs some additional figure-in'...

TCB
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