BB Coaxial

[knappengineering]

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 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

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

[BigJon]

Very nice gun there and it sounds powerful too 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.

[knappengineering]

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.

[elitesniper]

pretty cool you used it when the glue was still drying?

[knappengineering]

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.

[SpudFarm]

that is just nice! realy good for a first piston gun! do you BTW got any idea on fps on that little gunni gun?

[knappengineering]

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.

[Novacastrian]

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.

[knappengineering]

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!

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.

[SpudFarm]

wow thats realy fast for a gun that small! that would hurt like fu(k!
keep it up dude

[knappengineering]

Yeah, thanks for the comments, I'll probably upgrade it soon so I'll post the new pictures as soon as its finished.

[Carlman]

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

EDIT: how big is your equilisation hole in the piston or does it leak around the sides?

[knappengineering]

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