I've had all day to think about this piston & I can't shift the image of the inside of the cylinder when I saw it had been sanded or something, it's much coarser than the original honing marks you see in cylinders. I think it would wear the plastic bands on a glided piston down in no time.
On another note I saw a one piece 30mm mount up for sale, listed as "medium", it looks identical to the one I found in a drawer the other day that I thought was "low". So I went & got it out, and to my amazement it's spot on for this new scope I bought, might have to ditch the flip up cover on the front but that's not a problem. Just need to work out which rifle gets it, or indeed if It requires the purchase of another rifle.....
.