SpudFiles

hi this will be my first pneumatic and i was wondering about useing a piston and how to
if i cant find out how to i will just use a simpel setup like this vv
http://www.sentex.net/~mwandel/cannon/air_gun.html

The wiki is your friend. Also there is a sticky in the pneumatic cannon discussion forum about piston valves with lots of images that would be a good place to start.

A piston valve will definitely give better performance than the ball valve that the marble gun you linked to has. They aren't all that difficult to make once you understand them.

Welcome to SpudFiles.

thanks
oh and just for every ones in fo im only 12(13 in 2 days tho) and i liv in
austraila (austraila have very strict fire ams laws) so i kinda limited
but i have shot plenty of guns tho cos i liv on a farm (my famliy doesn't have 1 tho)

i was hoping to use this as more of a sniper so how long should the barrel be and i will probaly be pumping to up to 300psi ish( cos thats all my compresher and cos last time i put somthing over 250psi i wasa in hospitall for 5 weeks,don ask it embarsing and i was 10)

Welcome to Spudfiles! Before posting again, make sure you read through the forum rules and posting rules. One of the rules is not to double post, and you have already triple posted. Just be sure to use edit next time instead of double posting. I wish you luck with your pneumatic.

Wow what compressor do you have that can pump to 300psi? If you are going that high make sure you use all metal parts. Bunnings will have everything you need. I suggest a coaxial piston design, illustrated here. Look around the showcase section for other coaxial designs. Welcome to spudfiles, its always good to have another Aussie on the forum