SpudFiles

That is a great way to look for proper fit. It is the say I sanded the pistons for the Mouse Musket. In the photo below, you can see some remains of one of the lines I drew on the side of the piston as it was lapped down to fit the breech. The piston was without an o ring so it depended on a very close fit to seal properly. As Gippeto mentioned, this works for the piston face too.

I fixed it. I did the water test and found that I had a full diameter leak. I sanded the end of the barrel on sand paper on plywood for about ten minutes. I used 860 grit to smooth it then polished it with 1500. It's a perfect seal. I also increased the travel of my piston to compensate for a somewhat loose sealing face. The rubber I used is hose splicing tape and it is absolutely leak free. Thanks for the help.

in the future, and excellent way to get a seal on a "Almost" true sealing face, it to place a felt disk or 2 behind your sealing face, so it has a little give. This has never failed me when a have a piston that almost seals.


Glad you got it working though! Congrats!