Piper , you are correct. The bore would have been plugged with a set size gauge ,if it entered passed 9" ,a gauge of the next size up would be used. If this did not enter passed 9" then the barrel would be marked at that size.So yes it would have been possible to have a barrel proofed at .719" but it in fact would have measured as .727". Gun makers would therefore try to bore as close to size as possible . The problem was highlighted with the impottation of guns like the Miroku in the 70's ,being metric size 18.4mm and 18.5mm [,724" & .728"]new guns that actualy measured .728" were stamped at .719" therfor being only .001" in proof.They then started to use an intermediate plug and marked to the next size up ,so it is possible to find Miroku's that are stampped at ,729" that actaly measure at .726".
With going metric they with increments of .004" .01mm bores are marked to the nearest lower size .
If you think you guys have problems with all this ,think how we feel ,we have had 6 changes to the rules ,marks and measurement since 1904.
