There's really not a translation. Imagine a broom handle, or something of the like, with a plug of 0.360" on one end and a plug of 0.350". Considering the stamp 108.49/108.49, it takes 108.49 spheres of lead with the diameter 0.350" to make a pound. A continuation of the 12 bore equals 12 balls but the fractional part is odd. Where are you going to get the fractional sphere?? When your unrifled tube passed by, 0.350" would pass the full length and 0.360" wouldn't pass the full length; thus the stamp. There are some tubes with seemingly odd stamps, but 0.37? sounds like either the fella pushing the plug the day of the proofing went the path of least resistance or there was some slight alteration during the making. On a smooth bore, 0.2mm/0.008" additional removal in polishing, or whatever, would require reproof. In an attempt to gather more knowns in solving a series of equations, a wax cast would be the next step. Just put a plug of paper/cotton/patch/whatever about 1" into the rifling and indefinitely borrow one of your wife's candels, using it to fill the chamber. Let it cool and punch it out. Measurements of the base, rim, etc. will help narrow the possibilities. I'd like to see your marks so could you post or email a pic of the flats and the area ahead of the flat?

Kind Regards,

Raimey
rse