Also, it is really cheap; it only cost me about $13
It really is a very simple, small scale pneumatic cannon. Overall length is about 18 inches, height is 4 inches. The barrel and air chamber are both removeable, which makes it easy to modify.
Step 1: Get parts
These materials I got at Lowes Hardware:
One 12-inch long 1/2-inch nipple (pictures 3 and 4)
One 1/2-inch ball valve with threaded ends (picture 6)
Two 1/2-inch close nipples
Two 1/2 inch elbows that are threaded (screw on) on one end and need to be glued on the other
One 2-inch to 1/2-inch threaded reducer
One 2-inch coupler
One 2-inch cap
These I got at Ace Hardwate:
One PVC Purple Primer (trust me, you need this if you don't want it to leak)
One PVC Cement
One roll Teflon (Plumbers) Tape
2 inches of 1/2 inch PVC pipe
8 inches of 2 inch PVC pipe
MAKE SURE YOUR PIPE IS PRESSURE RATED!
These I got at Schucks Auto Supply:
One pack (icludes two) tire replacement valves for a .453 rim hole (picture 2)
Step 2: Get Taping and then Screw!
Do the same thing to get other bend connected to the 2-inch to 1/2-inch bushing. Again, you should not be able to see the nipple once they're screwed together.