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BB Coaxial

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Unread postAuthor: knappengineering » Fri Jan 04, 2008 4:37 pm

This is my first working piston gun, and it was surprisingly easy to make. I threw it together in about 10 minutes and it works great! It embeds bbs about 2 inches in gelatin at 30 psi. I'm gonna fire up the compressor and test it at 100 psi when its dry :twisted: Let me know what you guys think for a quick, first piston gun. All comments and criticism welcome. And i know about the messy primer job in the front, remember it only took 10 minutes :wink:

Specs:
-3/4 inch body
-1/4 inch ball valve for filling/pilot
-barrel is 1/4 inch pex tubing
- piston is a solid rubber stopper that fits perfectly in 3/4inch pvc

Edit: This thing is powerful! It went all the way through the gelatin at 60 psi and cracked the plastic behind it :lol:
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Unread postAuthor: BigJon » Fri Jan 04, 2008 5:26 pm

Very nice gun there and it sounds powerful too :D The only thing I see wrong is that your piston isn't servicable but oh well.

Edit: Or are those plastic screws on the endcap? I can't really tell.
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Unread postAuthor: knappengineering » Fri Jan 04, 2008 5:33 pm

Thanks for the comments. You are right, the piston isn't servicable but it works perfectly and its just rubber so I don't think there is anything that can go wrong with it. About those "plastic screws" that is just hot glue that the end cap was sealed with during testing. But now since it works I pvc glued it.
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Unread postAuthor: elitesniper » Fri Jan 04, 2008 5:37 pm

pretty cool you used it when the glue was still drying? :shock:
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Unread postAuthor: knappengineering » Fri Jan 04, 2008 5:40 pm

Yeah I did, but i wasn't too worried about it. I only took it to 60, and I could do that before it was glued without it blowing apart, but usually on my cannons I let it dry first. :wink:
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Unread postAuthor: SpudFarm » Fri Jan 04, 2008 5:49 pm

that is just nice! realy good for a first piston gun! do you BTW got any idea on fps on that little gunni gun?
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Unread postAuthor: knappengineering » Fri Jan 04, 2008 5:51 pm

Thanks. I'm sorry, I don't know of the top of my head and I don't have a chrono. But I'll try to figure it out and I'll let u know.
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Last edited by knappengineering on Fri Jan 04, 2008 6:47 pm, edited 2 times in total.
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Unread postAuthor: Novacastrian » Fri Jan 04, 2008 5:54 pm

Very nice indeed, it reminds me of my first (and only) pneumatic.
How thick was the chunk of gelatin that you shot at?
I'm just going to have to make a larger one when i get back to work i think, they work really well as you have just found out!

My only suggestion would be to pilot it with a blowgun to improve your accuracy. Nice work.
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Unread postAuthor: knappengineering » Fri Jan 04, 2008 5:59 pm

Thank you very much. The gelatin was 3 inches thick. I have other pneumatics that are much larger (1.5 inch barrel) with modded sprinkler valves but this shows me the efficiency of pistons compared to sprinklers. Yeah, that is a good idea, I want to get a brass 1/4 inch T so i can fill with the ball valve and shoot with the blowgun. Thanks again everyone for all the great comments! :D

Edit: The fps might be more like 493 at 60 psi, because I forgot to change the dead volume.
It would be around 617 at 100 psi.
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Unread postAuthor: SpudFarm » Sat Jan 05, 2008 11:32 am

wow thats realy fast for a gun that small! that would hurt like fu(k!
keep it up dude
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Unread postAuthor: knappengineering » Sat Jan 05, 2008 12:01 pm

Yeah, thanks for the comments, I'll probably upgrade it soon so I'll post the new pictures as soon as its finished. :D
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Unread postAuthor: Carlman » Sat Jan 05, 2008 12:55 pm

that is EXACTLY what i wish to do in the near future except find a barrel that fits these candy i found at red dot, hard as rocks almost broke my teeth trying to eat 1, and they dont taste god anywayz so yea ill get onto it soooon.

very nice gun by the way :D

EDIT: how big is your equilisation hole in the piston or does it leak around the sides?
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Unread postAuthor: knappengineering » Sat Jan 05, 2008 11:18 pm

It doesn't have an equalization hole, but the rubber stopper is a perfect fit and leaks around the sides a little bit.
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