Jeff;
Just recently another poster had a Drilling with this same mark on the rifle barrel. briefly the 67/49 is the "Gauge" of the bore which was marked prior to 1912. 67.49 gauge calculates to a bore diameter of .410" or 10.41mm. Note that this is the bore diameter, not groove diameter so you are likely looking at a bullet of approximately 10.75mm or .423".
11 mm converts to .433" so not likely quite that large but not to be totally counted out either. "I THINK" that the way these gus were marked at this point in time the bore could be up to anything just short of accepting the next size up which was 62/78 or .420" (10.67MM) so an 11 mm cartridge is not totally out of the question.
To determine exact cartridge for which it is chambered I would highly recommend slugging the bore & making a chamber cast to determine exact dimensions of the chamber & bore. You can scroll down to page 2 & find the other post which concerns a Drilling for additional comments.
