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Semi Automatic Blowback Paintball Launcher

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 Automatic Blowback Paintball Launcher

Unread postAuthor: Lockednloaded » Sat Jun 19, 2010 4:57 am

I have been designing and redesigning my upcoming launcher, and I have now abandoned the pneumatic cylinder option. So I decided to go with a blowback design for the loading mech. It seems simple enough, but I'm having some second thoughts about it. I fear that it may chop up paintball randomly, that the spring will have to be adjusted depending on firing pressure, and that the blowback option will decrease the power and efficiency of the launcher.

Now, my expectations for the launcher:
I want it to be fully adjustable, from close range messing around, to field legal speed, to bonecrushing, ass kicking power :lol:

Here is the current design, it was made for functionality, adapted for looks.
The barrel will probably be longer and a real hopper may be added

Image

Aluminum flashing will be made into a body:
Image

eventually, I hope to have this
Image
Comments, thoughts, critique, and improvements
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Last edited by Lockednloaded on Sat Jun 19, 2010 7:14 am, edited 1 time in total.
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Unread postAuthor: psycix » Sat Jun 19, 2010 5:40 am

If you want to use it for real paintball I suggest to use a real (high quality) paintball barrel for optimal accuracy.
How will you prevent the bolt to chop the balls?
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Unread postAuthor: Lockednloaded » Sat Jun 19, 2010 5:48 am

I'm not an avid paintball player, so a precision barrel will not be need do to the fact that I have limited tools so working with 3/4" CPVC will be much easier.
To prevent chopping the bolt will be totally rounded and probably made of cast hot glue or cast epoxy. I will put a slight angle on the top so that worse case scenario it will just dry fire once. The back threaded plug will make it serviceable though if paintballs start popping.
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Unread postAuthor: iknowmy3tables » Tue Jun 22, 2010 9:00 am

what pressure are you running it at, blowbacks don't work well at lower pressures
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Unread postAuthor: jackssmirkingrevenge » Tue Jun 22, 2010 9:09 am

iknowmy3tables wrote:what pressure are you running it at, blowbacks don't work well at lower pressures


... unless you have a heavy and/or tight projectile ;) since paintballs aren't that heavy, I suppose you'd need a tight barrel.
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Unread postAuthor: Lockednloaded » Tue Jun 22, 2010 4:53 pm

i will be running about 120 psi, and the spring will be very weak. someone else built one with a SV that worked at just 40 psi, I believe it was Tetsuo315
:EDIT:
will the weight of the bolt affect the lowest working pressure? and how high could the ROF be with this design?
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Unread postAuthor: Lockednloaded » Mon Jun 28, 2010 1:15 am

sorry to double post, but I haven't got an answer and I'm beginning to start in on the build itself. my main questions are: will a well lubed cast hotglue bolt blow back with weak spring strength a low pressure when firing a paintball from 3/4" cpvc; will the length of the barrel affect how easily the bolt will blowback; will paintballs get chopped up in the ammo feed with this desgn

thanks for any help, I know this is a topic that not many have researched, but any body who understands this project is enough of an expert for me :lol:
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Unread postAuthor: POLAND_SPUD » Mon Jun 28, 2010 1:23 am

will the length of the barrel affect how easily the bolt will blowback

yes, but don't ask me for any specific numbers regarding this :wink:


will paintballs get chopped up in the ammo feed with this desgn

That's also a tricky question... I am sure that you could delay the return stroke with the use of a simple check valve that will limit the speed of the piston

It would be better if you could use slightly higher pressures too. If you are using lighter ammo then it might be a good idea to make up for that with higher pressures
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Unread postAuthor: Lockednloaded » Mon Jun 28, 2010 1:29 am

i will be sure to get a longer barrel than, thanks.

with longer piston travel i could delay the return stroke, but this would also give it time to accelerate, chopping ammo. so its gonna be tricky...

by higher pressure what do you mean? its relative, to me over 16o is pretty high, but for someone with a fridgy we're talking over 400. i would like to use a maximum of 100 psi because thats what my co2 reg maxes out at
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Unread postAuthor: POLAND_SPUD » Mon Jun 28, 2010 1:38 am

well I think there is only one way to find out... jsut make sure your gun can handle let say 300 or up to 400 psi

but this would also give it time to accelerate, chopping ammo. so its gonna be tricky

ohh I think I haven' explained it too well... you can use a check valve that will let air out from behind the piston but it will restrict flow on the return stroke...
so the piston can move freely backwards but as it returns to its original position flow restriction will slow it down

it doesn't have to be a real check valve as you don't really need to limit the flow completely... anyway that's just a suggestion and it might not be needed
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Unread postAuthor: Lockednloaded » Mon Jun 28, 2010 1:45 am

POLAND_SPUD wrote:well I think there is only one way to find out... jsut make sure your gun can handle let say 300 or up to 400 psi

that depends, how far past the rating can I take my three-way, it seems to be of solid metal construction, but I don't particularly like exploding valves

i see what you are saying about the piston, would a hole drilled through the piston with a flap of rubber be too crude?
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Unread postAuthor: jackssmirkingrevenge » Mon Jun 28, 2010 1:56 am

Lockednloaded wrote:with longer piston travel i could delay the return stroke, but this would also give it time to accelerate, chopping ammo. so its gonna be tricky...


In one of my combustion cartridge breech prototypes, I swapped the coil spring for an air spring with adjustable pressure, the friction of the piston helps to delay the blowback of the bolt which should avoid chopped ammo.

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Unread postAuthor: Crna Legija » Mon Jun 28, 2010 2:32 am

well btb was feeding his Pnuschnikov with like 300psi.
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Unread postAuthor: Lockednloaded » Mon Jun 28, 2010 3:40 pm

@ JSR:
i think a coil spring with a bolt for adjustment will be fine for this application, but if the won't work I'll look for a syringe tube and some low viscosity epoxy.

@-_- :
i think his was a forced blowback design
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Unread postAuthor: Lockednloaded » Thu Jul 01, 2010 8:19 pm

sorry for the double post, but i have redesigned the loading mech in the principle of KISS. I think it should work well, and never double feed, but i don't know for sure

here's a picture, it is a paddle tha swings up while fireing preventing double feeds

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