Drilling Guy,
Your drilling was made after early 1893 when they started proofing them, and before 1912 when they started marking bore(not groove or bullet) diameter in mm instead of the old gauge measurement. The mark 62/78 equates to about 10.67mm or around .4198". This is bore diameter, not bullet diameter. Of course, many were different, but a rule of thumb is to add about .008" to bore diameter. This would result in a bullet diameter of about .428". The use of 444 Marlin cases point to a cartridge in the LK series, and the trimmed length of 52mm points to the 11.15x52 LK Express, but that bullet is listed as 11.2 mm which is larger than that guessed at by the rule of thumb. You should trust the chamber cast and/or barrel slug. There are a couple other possibilities and when you measure the chamber cast and groove diameter, we can look again.
Mike
