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Gas Operating Ammo Feeder (Semi Auto)

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: MRR » Tue Mar 03, 2009 12:03 pm

I think the main problem, when you operate at low pressure, is that the pressure escapes through the "catching holes" before the piston is able to overcome inertia and friction (thanks POLAND_SPUD for that idea).

So I'm going to build a simple check valve system to prevent losing pressure.

Image

The holes will be covert by elastic bands or simply rubber, so the air will go into the pressure catch but is not able to escape.
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Unread postAuthor: POLAND_SPUD » Tue Mar 03, 2009 2:40 pm

well this might work...

unfortunatelly the problem is that in your design the check valve would trap air and the piston/aircylinder would move but you would need a seperate valve to release the air...

note that you don't know if it would work in the first place yet you have to add an additional part just to release air

so to sum it up, you would probably need a well made piston/air cylinder to make this work as well as a check valve and a valve for releasing air to let the piston/aircylinder retract and you still need a firing valve (+optionally a pilot valve if you want to use a QEV or piston valve)

so 4 to 5 parts


in my design (note - I don't claim it's mine.. let say it's a collective work :wink: ) you need less parts... you only need a 3 way valve, an air cylinder and a QEV/piston valve

so only 3 parts

what's the point in taking air from the barrel when you can use air from the chamber without lowering performance ??


no offence I am not criticizing you... in fact we've all been where you are now... quite a lot of people wanted to build a design similar to yours but AFAIK no one has ever succeded but there were several guns based on 'my' design
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Unread postAuthor: jackssmirkingrevenge » Tue Mar 03, 2009 2:51 pm

No need for the check valve complication, just make sure your piston is big, friction free and light enough to take advantage of the little burst of pressure that is available to it. After all, all you're doing is pushing back a sleeve against a relatively weak spring, there are no massive forces it has to counter, not does it have to travel more than a couple of centimetres.

I've pooh-poohed this idea in the past in terms of spudguns, it won't work if you copy an assault rifle mechanism directly but I think if you adjust the dimensions to allow for the lower pressure, it might just be feasible.
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Unread postAuthor: MRR » Tue Mar 03, 2009 3:13 pm

@POLAND_SPUD
I simply like the idea of "recycling" pressure.
When so many people tried it and didn't succeed it's even more a challenge.
And if I fail than I'm not the first. I always have more fun building things than actually using them.

@jsr
I will build the piston rod as light as possible. I was thinking of a 2 - 3mm aluminium rod, not sure what I use as a piston though.
And for the check valve.... I will have to drill some holes anyway so I give it a try. Maybe it could give the construction the "kick" it needs and it's pretty easy to make.
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Unread postAuthor: jackssmirkingrevenge » Tue Mar 03, 2009 3:29 pm

If you do put a check valve, remember that the air has to bleed out of somewhere, otherwise the piston will never reset. I would avoid it personally.
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Unread postAuthor: MRR » Tue Mar 03, 2009 3:36 pm

I simply drill a release hole in the housing where the piston shall stop.
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Unread postAuthor: POLAND_SPUD » Tue Mar 03, 2009 3:46 pm

@mrr acctually I've tried to build something similar but it failed...

the idea of recycling air is cool but IMO using pressure of air in the chamber is better becasue you don't lower the performance in any way...

recycling air has only one advantage - it could silence the gun to some extent (but don't expect it to be better than a homemade silencer of similar volume)

the design you want to try isn't in any way better than mine.. it would either have similar or worse performace yet it would be several times more difficult to build
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Unread postAuthor: jackssmirkingrevenge » Tue Mar 03, 2009 3:50 pm

MRR wrote:I simply drill a release hole in the housing where the piston shall stop.


... and what happens when the piston passes that hole? Make sure it isn't 100% airtight, otherwise it will hang.
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Unread postAuthor: MRR » Wed Mar 04, 2009 11:44 am

We will see... I'm really in the mood to build this. I rather build something by trail and error than not trying it.

And by the way...if I don't get it to work I have all the parts to build a nice pump action reloader.
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Unread postAuthor: THUNDERLORD » Tue Apr 21, 2009 11:34 am

Old post but I was thinking again of venting spent, inert gasses from a hybrid with a blow forward bolt attached, an this post's concept came to mind.

I think this has potential for opening a valve to vent the chamber, since it is near the end of muzzle, the chamber would vent after the pressure has done it's job on the projectile!!!
Perhaps even a small check valve would work.

I've explained my idea more in reply Here (pg. 1) 8)

EDIT: BTW, forgot to mention that a hydraulic system could be used in a chamber or barrel design similar (especially to prevent chamber leakage).
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