this is a mini pneumatic i made from spare parts in 15minutes.
its a 1/4" barrel 1' long which threads into an adapter for a 1/2"ball valve and then i scrwed a pva bottle into the other end of the ball valve.i will use a 2.25litre coke bottle but i dont have one on me right now so here are some pics.the schrader valve is in the very end.
btw i put a apple ipod video in the picutres to use a size reference
i havnt shot it yet as im going to get a bigger bottle, with that pva bottle it wont do shit lol