I am in the process of building my first pneumatic air gun which is a mini coaxial. I have made the piston out of a short length of pen cap which has been filled with hot glue and has a piece of 3mm rubber as the sealing face. There is no visible gap but It slides easily down the tube. It also won’t...

I’m about to glue the schrader valve into my mini coaxial and was wondering if I should remove the rubber from around it. Would it be safer to remove it and then epoxy it in or just leave it as I’m only planning on taking it to 200 psi max. Thanks for the help