This is a fairly easy way of making an awesome 1/2 inch pnuematic pvc luancher.
Step 1: What You'll Need
most of these things can be found in any hardware store besides the bike pump, as for that you're on you're own, I've had that mounted on my road bike for several years and is probably discontinued by now, but you could probably find another one in a bike shop that'll work for not too much.
*all pvc is 1/2 inch in diameter*
atleast 2 feet of pvc pipe
1) 2 liter bottle
1) pvc cement
1) electricians tape( or any other type of strong tape, but I like the feel of electricians tape on the handle)
1) pvc ball valve
Step 2: Assembly
Assembly is pretty simple and straightforward- the pump I have fits snugly inside the 1/2 inch pvc pipe. as you can see first of all you should pvc cement together the 3 pvc pipes to the T one side to the 2 liter bottle one side down to the pump and one side with a small section of pvc going to the ball valve. you can make any of these sections any length you like, but the longer the barrel (up to about 3 1/2 feet long) the better. pvc cement the pump, 2 liter bottle, and ball valve to their appropriate pipes. but do not pvc cement the barrel tot he ball gauge because It's easiest to remove the barrel to put the ammo in.
Step 3: Have Fun!
AA batteries (must be wrapped in duck tape a bit to be perfect fit)
Baby cut carrots
Mini Marshmallows (good for shooting indoors and not destroying anything )
I am not Liable for any injuries that might happen to come about because of this instructable..
and do be safe- don't shoot AA's or marbles at any one... it could really hurt(kill). =p
Here's the video displayed in my animated gif.