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semi auto help

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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semi auto help

Unread postAuthor: beastmode986 » Mon Jun 18, 2012 7:41 pm

ok so for my next project i want to make a semi auto.I ordered my qev and it is stainless steel :), Im expecting it to arrive next week. Now im still considering a single shot but this might be alot more fun.
I want to make a bullpup semi automatic that is magazine fed.I am going to use marbles as ammo most likely but i might want to shoot something thats a little smaller any suggestions for ammo? I am also considering 9mm ball bearings. Now the main issues i will run into are
1. making a blow forward bolt
2.making a trigger mechanism

Now i know you guys are thinking well why dont you use a slide valve well because im not sure if it will withstand the high pressure from my air source
(20oz co2 tank) now i guess i could use a regulator but if i regulate it to 100 psi i would want more power than that would give (i want around 60+ft lbs of muzzle energy) so any suggestions are appreciated


EDIT: ggdt says if i use 300 psi with a 7gram marble i will have 67ft lbs but the gun would be very inefficent
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Unread postAuthor: sagthegreat » Mon Jun 18, 2012 8:23 pm

Lol we are doing the same project right now lol, for the trigger use a semi auto blowgun mod, for that look at wyz's guns


EDIT- and you will definatlly need a spring in the qev and maybe a hole in the piston?
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Unread postAuthor: beastmode986 » Mon Jun 18, 2012 8:39 pm

why a hole in the piston? i understand the spring part but how would a hole help?
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Unread postAuthor: Crna Legija » Tue Jun 19, 2012 1:50 am

get a slide valve used in paint ball and with a slide valve you don't need a hole in the piston no spring ether.
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Unread postAuthor: sagthegreat » Tue Jun 19, 2012 7:00 am

just curious, if you were to do it with the semi auto blowgun method, would you need a hole?
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Unread postAuthor: Crna Legija » Tue Jun 19, 2012 7:04 am

You only need that if you chamber fill, so long as you use a tee to fill and pilot from the pilot size you don't need any mods to the piston
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Unread postAuthor: sagthegreat » Tue Jun 19, 2012 7:14 am

you would need to mod the piston for multishot, because it needs a way to autoclose, and you would need a spring
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Unread postAuthor: Crna Legija » Tue Jun 19, 2012 7:23 am

sagthegreat wrote:you would need to mod the piston for multishot, because it needs a way to autoclose, and you would need a spring


Read what i wrote up before, then think to your self am i going to fill via the pilot port or chamber side?
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Unread postAuthor: qwerty » Wed Jun 20, 2012 10:58 am

Respectively, you're not going to get many shots at 60ft/lbs with a semi-auto gun, You would end up using the CO2 very quickly.
If i was you i would go for either a small caliber hammer or slide valve gun, something like mine with regulated CO2 to about 200-300psi would be ok for smaller calibers with a good amount of power.

If you're not going to regulate it, most QEVs and slide valves will blow at those pressures so a hammer valve gun would be more suitable.
Goodluck. :)
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Unread postAuthor: Goats spudz » Wed Jun 20, 2012 4:58 pm

qwerty wrote:most QEVs and slide valves will blow at those pressures
My cheapo Qev and Slidevalve work at 1000 Psi.
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Unread postAuthor: qwerty » Thu Jun 21, 2012 1:55 am

Get me a link to that slide valve pl0x, most are rated to about 12 bar and the o-rigns probably blow out or leak at about 400psi, not too sure though.
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Unread postAuthor: jackssmirkingrevenge » Thu Jun 21, 2012 2:40 am

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Unread postAuthor: sagthegreat » Thu Jun 21, 2012 3:18 pm

Aww come on I just spent the last 5$ in my paypal, i shouldve got that valve
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Unread postAuthor: beastmode986 » Sun Jun 24, 2012 3:30 pm

jsr i dont see how i can use that slide valve, i dont see any threads?
also i want to shoot .25 cal pellets or .22 but it seems like it would be very difficult to make a magazine to feed them. what do you guys think?
The bad thing about me making a hammer valve is i am not sure wha to use to make a hammer, Even if i made it bolt action i still wouldent be to sure.Every time i have attempted to make a hammer valve in the past it did not work correctly, I could never get it to seal any tips??? i would love to run unregged co2 but now that i think about it more it would be very unefficent so i will probably get a regulator.


EDIT I NEED HELP

just got my qev but it wont seal. everything is in correctly but it leaks out of the barrel.
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Unread postAuthor: beastmode986 » Sun Jul 08, 2012 2:35 pm

Sorry about this double post but i got my qev to seal but i want to fill it through the air chamber, what do i do so i can fill it that way? i saw threads saying make a small hole in the center but then it would leak out of the barrel wouldn't it?
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