Nobody here is going to 'steal' the serial of your single-shot 100 year old+ hunting rifle to misuse, I'm pretty certain. The guy with the club is Hercules, BTW. I've had a look at the page you link to, and you seemed to have nailed it pretty well. The metric bore that you measured in imperial works out at 8.83mm. However, depending on where you made the measurement - lands or grooves - it could also be about fifteen metric cartridges of between 8 and 11mm, so you'd really need to make a chamber cast to find out what it really is.
The 108/40 is an early form of bore description, and suggests that your rifle is nearer that 11mm calibre you noted. Slugging the barrel will definitely help. This article by Steve Meyer is very helpful here -
QUOTE - The most frustrating but perhaps the most useful marks of the 1891-1939 era are the various sets with just numbers present. The two most common sets of numbers applied were bore dimensions and actual proof dates.
Rifles from later in this era are sometimes stamped with a bore (not groove) diameter in millimeters, the most common being 8,8mm for one of the 9.3mm cartridges and 7.7mm for one of the many 8mm cartridges. Some rifles will also have chamber length marked along with bore diameter. Many earlier rifles will be found with numbers indicating the "gauge" (number of bore-sized round lead balls to the pound) diameter of the bore (not groove diameter).
For instance, a number in the 95-105 range would indicate a bore diameter near .360" and hence likely to be a 9.3mm chambering of some kind, while a number in the 170s would indicate an 8mm of some kind. I've even seen rifles marked with a pair of gauge marks that calculated so close to the actual bore and groove dimensions it was astonishing!
There were several commonly used rifle gauge marks such as 172.28, 156.14 and 141.95 that correspond to 0.010” increments starting at 0.300”and getting larger that followed British conventions. Very often this style gauge mark will be of the form 172/28 rather than with a decimal point or comma.
Unfortunately, with German rifle barrels of this vintage, it is nearly always necessary to make a chamber cast to determine the actual chambering and bore dimensions. Be safe by being certain! END QUOTE, with thanks to Steve Meyer.
tac
