Eureka! As the old Greek exclaimed. I found the answer, while looking for something else. In Vic Venters' "Gun Craft" article in Shooting Sportsman, Mar/Apr 2012:
"For example, under the old Imperial-era Rules (1954-89 "tons" era), a gun could remain in proof so long as its bore was enlarged no more than .010". By contrast, guns proofed under the 1989 CIP Rules (and those that have followed) remain in proof through enlargements up to 2mm--which is equivalent to .008".
I think either Vic or the copy editor mislaid a decimal point in that quote. Should be 0.2mm equivalent to .008". So the new metric measurements still allow some "slop"--just not quite as much. It could start life marked 18.5mm (the standard) and have been enlarged up to 18.7mm without requiring reproof and remarking.
Last edited by L. Brown; 02/13/17 10:37 AM.
