Step 1: Materials
1.5m (5ft) of copper pipe
One 22mm elbow
Two 22mm endcaps
Two 22mm elbows
One 22mm Ballvalve
One tire valve
All pipe in this project can be any diameter, however, as the pipe size increases, so does the bill .
A good chamber:barrel ratio by volume 1:2, however you can change this to suit your needs. A gun with a barrel which is either too long or too short will not be more powerful, but rather less. You can use the Gas Gun Design Tool Tool to find out this length. The ".GDT" file is the saved data for my gun.
As a UK based user getting copper is simple. Many plumbing and hardware stores stock it. I highly reccomend BES Gas and plumbing supplies. I suspect the situation is similar in the US. Ballvalves are very common, and can be bought from most plumbing stores.
Flux and solder will more than likely be available in the same store.
A tire valve can be got from any auto store, or ebay. I got 10 snap in tire valves off ebay for �3 posted. nd they are perfect for this project.