Today, while sitting in the floor of Home Depot I had an epiphany. I was trying to figure out a way of making a low cost piston gun that was powerful, simple, and anyone can build. While searching Spudfiles, I found FoxxLord's (he gets credit for piston!!!!) 3" barrel sealing piston valve tutorial. I was amazed at the low cost and simple design of the valve. I love his idea, but its fatal flaw lies within the method of it's chamber. In a barrel sealing valve setup, the barrel goes back into the chamber, meaning the gun must be very large to have a significant chamber. My method involves putting a tee between the barrel and piston valve. In doing so, my design allows you to branch off of the bottom and have a huge 4" chamber. When you dump air from behind the piston, the piston gets forced backwards against a spring or bumper, etc. When the piston goes back, the barrel gets opened up to the full brunt of a massive amount of high pressure air.
Needless to say, this idea would be quite powerful, and could be made for no more than $60.
Here is a drawing of the idea. I would appreciate feedback.