I am proud to have finally built a piston valve in the form of my 3/4 barrel 2" barrel coaxial. That gun, unfortunately had a leak that required some rebuilding. i just re-did the front end and tomorrow will see if the leak was fixed. The leak was minor, however, and i got to test the piston a fair amount. I am now extremely convinced in the superiority of pistons, while my modded sprinkler makes a long kutha-wump noise, and definitely does not empty my chamber instantly, my piston made a very noisy crack and empties the chamber instantly. I am however, disappointed with the 3/4 barrel as i really like to shoot potatoes, and 3/4 cut potatoes don't go very far. I would like to build a barrel sealing tee piston. Im not going for any fancy o-rings or super performance, i pretty much just want to contain the back end of my coaxial gun in a tee with 1" barrel porting. Nothing amazing, but i am very confident it will blow my sprinkler out of the water. My basic idea is to sand out the stop in a tee and push the pipe in it a little further in than it is meant to go. The to barrel out pipe will go just past the pushed in piston tube. I believe this has been done before and successfully, but i wanted to make sure my design is good. I want to stay away from hot glue pistons though, their tight fitting might give a performance boost but i just hate the idea for some reason. Heres an image, if this works it would cost less than a sprinkler valve and give many times the performance, i hope. The piston would be identical to the 1 1/4 cap+bolt+rubber washer on my coaxial. i could even use the same fill/trigger section. So, does this look like it would work? i think it looks solid.

If this works i would probably write a how-too on it. I would gladly encourage any one here to build a co-axial piston gun like mine. With parts that can all be purchased from lowes it can be made extremely easily. This forum tends to (not purposefully) make it appear very hard to make piston guns. this is probably because alot of topics are about super tight fitting o-ringed check valved super pistons. A looser but still very well performing piston can be made very easily. I already have shown myself how easy my coaxial was, but something like this would be plug-and-play and probably appeal to the masses.
Edit: This is almost the exact housing i plan to use, though i would not have the uber fancy piston.
http://www.spudfiles.com/forums/tibs-la ... t7933.html