Am I right in thinking that the piston in an old BSA Imp Mod D Light Pattern should not scrape the sides of the cylinder ? It seems the piston on this gun is slightly out of round and the front end of the piston is quite a bit more than an interference fit on one side only, so just thought I'd check before spinning it up in the lathe. It's not tight but all my polishing of the piston front end has been ruined with the scuffing in the cylinder.