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Semi Auto Design Help

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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Semi Auto Design Help

Unread postAuthor: PaperNinja » Sun Jun 17, 2012 8:19 pm

I'm (obviously) pretty new to these forums, but I was looking around and it seems like a pretty useful place :). I have already made a cloud BBMG (at a friends house right now) and I thought it would be cool to make a semi automatic. (the bbmg uses too many bbs... I have to buy the biodegradable ones) After some research on these forums, I found just the standard design, 3 way valve attaching to QEV with small brass chamber. I'm hoping to use 12 gram Co2 cartridges as my air supply. The problem is, I don't know a good way to prevent double feeds, I don't really want to do a blow forward bolt, as someone had pointed out in a thread I found that it would waste energy that could go to the pellet. If blow forward bolt is really the only good option, then I'm willing to go with it, but I was hoping to find something a little more efficient. Another thing is that the pilot air to trigger the QEV just seems like a waste to me... is there anything interesting or good I can do with that? I would prefer not to have to do a lot of modding to valves and whatnot, I'm pretty capable, but I"m still fairly new to air guns. If it is relevant, I have tools such as drill and hacksaw etc, but nothing fancy like drill press (maybe a lathe sometime in the future).

Thank you for reading :)
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Unread postAuthor: Lazyboy » Sun Jun 17, 2012 10:06 pm

The blow forward bolt does not waste air, as the air used to load the BB is then used to propel it down the barrel.

Make the blow forward bolt to the minimum size required for the gun to operate.

Hope this helps
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Unread postAuthor: Lockednloaded » Sun Jun 17, 2012 10:11 pm

You seem to be really concerned with air usage (well co2 usage in this case) if you're so concerned about this, a hammer valve may be your solution. As for the loading mech, a simple detent+tee mag should suffice. Or even for ultimate efficiency, go valveless.
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Unread postAuthor: jackssmirkingrevenge » Mon Jun 18, 2012 1:50 am

Lockednloaded wrote:You seem to be really concerned with air usage (well co2 usage in this case) if you're so concerned about this, a hammer valve may be your solution. As for the loading mech, a simple detent+tee mag should suffice. Or even for ultimate efficiency, go valveless.


My thoughts almost verbatim :)

Have a browse though this thread: http://www.spudfiles.com/forums/valvele ... 21364.html
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Unread postAuthor: PaperNinja » Mon Jun 18, 2012 5:53 am

I'm not sure I want to try the valveless, I wouldn't want to have to worry about the friction of various projectiles, and I wouldn't want to have the rubber (or whatever substance I use) dry out or get wet etc meaning I would lose power. I could try a hammer valve, but tbh I don't really understand what it is and I haven't found a place that really explains it.

Lazyboy wrote:The blow forward bolt does not waste air


You positive?
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Unread postAuthor: Lazyboy » Mon Jun 18, 2012 6:48 am

All the air released goes down the barrel, but the amount of air released depends on the activating valve.

I made this gun http://www.spudfiles.com/forums/viewtop ... tml#320537

But found the blow gun released to much air to be a practical airsoft gun.
I am now working on ways to make a pulse valve or use a small 3 way valve to conserve air
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Unread postAuthor: PaperNinja » Mon Jun 18, 2012 6:56 am

Another problem I've discovered, I was looking at http://www.spudfiles.com/spud_wiki/inde ... _cartridge , and realized that with such a small chamber the PSI would be pretty huge, and I don't know if my QEV (aluminum square-type) can take that kind of pressure. I don't need to use the 12 gram cartridges, but does anyone have a link to a (fairly) small regulator or have a better fix? I don't want to be carrying around 10 pounds of PVC just for an air source... I already have to do that for my BBMG and it isn't fun... (yeah I know I'm kind of an idiot for not realizing that I would need a regulator earlier)

To solve both of my problems, could there be some way that I could use the pilot air to push forward the blow forward bolt?

Thanks for the help
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