Pump Action Combustion.

[rna_duelers]

I have been eyeing off the Tippmann C3 for a while now and have though,why not try and make my own little pump action marble/paintball gun.Using the pump action to load,fuel,exhaust the cannon.I have a most of the parts lying around and hopefully building this cannon will cost next to nothing to make as I have no money and will not have any for a while.

I'm leaning towards an over-under style chamber/barrel for it with a 3/4 brass chamber 120mm length and a barrel that is maybe 30-40cm in length.

Here are some rough drawings,any ideas on the project will be great and metering the fuel,thats a problem..

ALso the piston could be exchanged out for a small hand pump to replace the air and to exhaust the chamber.

[psycix]

What is the 1way valve for, it isnt needed.
And hey if you do it good: you can muzzle load projectiles and suck em in with the piston
Would be cool.

[Skywalker]

I built a small-scale gun similar to what you are thinking about. The main problem I had was that I had to pump it several times to get all the old air out, which was a pain, and resulted in inconsistent firing. Ideally, you should have a check valve to let fresh air into the space behind the piston as you push it in, and then have a checkvalve in the piston so that you compress the air behind it as you pull back, and it flows through the piston. In your design, what's to keep the exhaust air in the barrel from being drawn back into the chamber? That is the easiest route for air to enter the chamber: the check valve will cause resistance but the barrel is wide open.

[NewB]

For rna_duelers design just put your hand over the barrel when you pull the pump and take your hand off when you push it.
Also be sure that you pull the pump as far as it will go or the pressure will blow that whole thing off.