Paul, I EXCEL at making single use tooling! Seems I've been doing it all my life
When I walk though my garage... er, shop, I pass by all the little things that will never see use again. Such a sad thing, for a machine, to have no use. I once spent a few days rummaging through a large metal chest that I acquired in a clearing out sale from a business that had been there for longer than I've been alive, and handling all the strange tools (some of which have contemporary equivalents, but the forms of these tools have evolved slightly over time), and wondering about their prior owners and wishing they could talk... so many scars and so much experience in them.
Would your prototype pistons have slightly larger diameters on the ring grooves, to push them closer to the walls? or did you select entirely different sealing rings entirely? Would you mind sending me or posting the dimensions here? I belatedly remember that I purchased a big hunk of brass that I was going to turn into a cylinder for my millennium europiccola... which I then sold... so now I have this big piece of brass staring wistfully at me
It COULD be a piston in disquise ...