Would I use McMaster part #90133A440 or #90133A435 for the sealing face on my 1 1/2" piston valve.
I ask mainly because I don't know if the one that's exactly 1 1/2" in diameter will be big enough where-as I could cut down on the 2" one.
P.S. <a href="http://xs513.xs.to/xs513/07102/roughsketch.png">Rough Sketch</a> of my cannon. Mainly the piston portion of it.