SpudFiles

I am building a pneumatic panzerschreck inspired by judgement arm's bazooka. It will be a piston valved coaxial. I get how it works, and I am almost done with the piston, but I was wandering if it needs like a spring behind it to keep it forced against the barrel to keep it from leaking air into the barrel.

And I was wandering what material I could use for the sealing face. I know that I can get something from mcmaster, but I really don't feel like ordering it.

If your asking these questions than you shouldn't be building one.

Gee Thanks

I am very new to pneumatics so just give me a break

Man I hate when people post that. "If you don't know one thing then you shouldn't be building this." We're all here to ask questions and show off. He's doing one of those actions, so lay off it and actually contribute.
Back on topic.
I would suggest neoprene for your sealing face. A lot of hardware stores carry it. I found some orange neoprene that is 6"X6". It has 1/8" thick and 1/16" thick in the same package. If you have an "Ace Hardware" nearby, check there.
If you can't find any neoprene, you can use basically any relatively hard rubber. Keychains work well, you know the thick rubber ones.

Your piston doesn't need a spring if it is filled from behind the piston. Otherwise, it will. I suggest filling from behind.

P.S. If you are going to shut someone down, at least use proper english. It's "you're" not "your." I'm not trying to flame you, I'm just sticking up for Arborman. We were all new to pneumatics once. Oh, and I just looked at all your posts. Most of them are put downs! Quit being a jagoff and help people out if you have an answer to their questions! Otherwise, be quiet!

Perfect

I have an ace hard ware right near me.

Thank you very much