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Semi-Auto BB gun

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: trollhameran » Thu Aug 21, 2008 2:25 pm

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Anyone ever thought about a design like this, I know it would work because I have tested the theory on a higher caliber gun.

Basically its a manually operated piston and bolt setup, where the bolt is actual barrel, and the piston is attached to the bolt.

The piston seals against the front of the chamber. When you pull the red trigger it pulls the piston and bolt assembly back, letting air out through the holes in the bolt, and blocking off the mag tube. The second piston stops the air flow from the source so that it only expends the air in the chamber each shot, this is to improve efficency. then when you release pressure from the trigger the air pushes both pistons back into place and moves the bolt forward again, allowing the next bb to drop into the barrel.
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Unread postAuthor: knappengineering » Thu Aug 21, 2008 3:29 pm

Sounds like an interesting idea as long as the seal around the barrel is sufficient so that it doesn't lose air when it starts to move back before it get to the hole in the barrel. I might also be somewhat inaccurate because the barrel moves.
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Unread postAuthor: trollhameran » Thu Aug 21, 2008 3:58 pm

you could have a sleeve attached to the chamber that the barrel would slide into, and have an o ring fixed to it near the chamber, and another toward the muzzle end, this would solve the sealing issue and also would provide stability for the barrel to keep it from moving around, which would make it more accurate.
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Unread postAuthor: SEAKING9006 » Thu Aug 21, 2008 4:00 pm

That's what I did for the X-ACS project. The sealing face of the piston is actually the side of the piston.
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Unread postAuthor: knappengineering » Thu Aug 21, 2008 4:01 pm

Yes that would indeed help, looks like an idea worth trying.
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Unread postAuthor: trollhameran » Fri Aug 22, 2008 1:02 am

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I just dug up this video of a really bad prototype a made of this idea, it didnt seal properly, and it was generally rubbish, but it proves that the idea will work.

I think it would be more effective with bb caliber though because of the smaller surface area on the end of the barrel, which would make it easier to push back, and allow higher pressures to be used.
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