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Air piston bb gun hybrid

This area is for the discussion of BB or airsoft sub machine guns, and or other small arms such as pellets.
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Unread postAuthor: Sticky_Tape » Sat Dec 20, 2008 3:34 pm

Very well I think I will start without holes and if I am unsatisfied I will drill them I have already casted the barrel in the cpvc I will make a 1/2'' piston (1/2'' tee) and clamp it into the end of the pipe and try it out see what happens.
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You can tell how awesome a cannon is by the pressure used.
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Unread postAuthor: ckman » Sat Dec 20, 2008 3:56 pm

if you use a bigger diameter chamber will the fps increase or decrease
oh and how would the piston come back after it has fired
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Unread postAuthor: Hotwired » Sat Dec 20, 2008 4:21 pm

With difficulty unless you put a valve in the barrel :wink:

I'm afraid the idea isn't new, I made a prototype design almost two years ago but only mentioned it a couple of weeks ago here.
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Unread postAuthor: Sticky_Tape » Sat Dec 20, 2008 6:57 pm

Turns out jsr mentioned the idea of having vent holes in the tube.
:x F***!
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Unread postAuthor: jon_89 » Sat Dec 20, 2008 7:34 pm

Finally I get how a light gas gun works. Do you know what pressure you would use to accelerate the piston. Could you use a tight spring to absorb the piston shock?
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Unread postAuthor: Sticky_Tape » Sat Dec 20, 2008 9:00 pm

I am putting this project on hold. I think I would use about 200 psi.
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Unread postAuthor: jackssmirkingrevenge » Sun Dec 21, 2008 2:00 am

Sticky_Tape wrote:Turns out jsr mentioned the idea of having vent holes in the tube.
:x F***!


Thanks ;)

Try it out, as I sugested you could make the piston driving element a combustion to give you a large diameter high momentum piston without complex valving.
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Unread postAuthor: ALIHISGREAT » Sun Dec 21, 2008 5:00 am

Just thinking about the length of this thing, if you were to make the piston acceleration a combustion (or hybrid which would be my choice) to get a decent length, you'd need to do an over under...
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Unread postAuthor: psycix » Sun Dec 21, 2008 7:17 am

If you want any decent pressure, you wont need the holes.
The pressure will only rise to 1 bar (14,7 psi) when the piston is already halfway. The most pressure will occur on only the last bit.

Make sure the pellet has enough static friction. (or use a BD)

Note that the holes will also vent out the driving pressure behind the piston after it passed!
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Unread postAuthor: Sticky_Tape » Sun Dec 21, 2008 9:40 am

That was the plan to have the driving pressure vent when the piston passesd the holes. What I am hoping is that the piston will accelerate very fast because there are the holes so that there isn't any building pressure on the front but then the piston will cover the holes and sort of create a pressure spike due to the high inertia of the piston and be the piston trying to compress the air in the compression tube part to no volume there will be a small amount oh hpa before the bb even moves due to the speed of the process and then the piston will completely pass the holes venting the driving pressure. wow run-on scentence
I think I am just going nto make this into a springer
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You can tell how awesome a cannon is by the pressure used.
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Unread postAuthor: Sticky_Tape » Mon Dec 22, 2008 7:09 pm

I pmed Gippeto to try putting burst disks in his break barrel gun and measure the volocity. The ammo he used was Crosman premier hunting pellets. The volocity of the gun without the burst disks was, in 5 shots an average of 450.2 fps with a max deviation of 7fps. a quote from Gippeto
Using one layer of aluminum foil, the average for 5 shots dropped to 416.4fps with a max deviation of 41fps.

I don't think anybody needs to tell me to use burst disks now.
Thanks Gippeto :)
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You can tell how awesome a cannon is by the pressure used.
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Unread postAuthor: jon_89 » Mon Dec 22, 2008 7:27 pm

That will be quit the spring.
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Unread postAuthor: Sticky_Tape » Mon Dec 22, 2008 7:31 pm

Naw it's going to be pneumatic.
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You can tell how awesome a cannon is by the pressure used.
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Unread postAuthor: CpTn_lAw » Mon Dec 29, 2008 6:41 pm

There is a solution...Make a two-sized piston. the side where you burst you air has to be wider than the side that actually compresses the air behind the BB. That way you don't have to have a tremendous pressure to push the piston, and the pressure build-up on the projectile's side won't put as much stress as a single diameter piston would have.
Twice the diameter will give you a 4:1 compression ratio etc....means that if you send 100 psi, the piston will actually remain accelerated until 400 psi are reached on the other side, then it will slowly decelerate, but if you play on the piston weight, you can actually get it to hit the cylinder end, creating a nice pressure spike...now imagine you use 300 psi air input....1200 psi equilization...quite powerfull isn't it?
You can also prevent the piston from coming backwards , putting some sort of one-way stopper. i'll do a drawing so you can see what i mean.
Hope this helps.
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