O rings give me a terrible time, hard to get a perfect seal using common tools. I've figured out a way to make a parachute seal out of a faucet washer and so far, they work remarkably well. I used it on the pilot side of my new piston for my t valve. Air goes in easily, but when it tries to go the opposite way, the edge of the seal flares out, making a perfect seal. On a 250 psi fill, a 10 gauge wad flew over 700 fps. I'll try to get some pics and possibly a video up later. Been having too much fun shooting.
Ultimately, I'm trying to make a balanced spool valve (QDV) using these as the seal instead of the troublesome o rings. This type of valve will give me a full bore valve seat, should yield greater power (.785 vs .625 diameter). It also offers mechanical actuation and no pilot air losses.