The above video demonstrates a simple and inexpensive airgun design that can be used with airsoft pellets or a wide variety of other projectiles.
6mm ID Brake Line (Test with airsoft pellet to check size)
1" x 4" PVC Pipe Nipple
1" Threaded End Caps (x2)
1/2" x 1 1/4" Spring (Approximate size)
Washer & Nut to fit the attached Brake Line Fittings
Brass Air Tank Valve (Schrader Valve)
Compact Bicycle Pump