very nice C.G: Haenel Modell 1900 I wish to have

when looking at the markings it seems clear that 10,75x68 was stamp later and this rifle was rechambered once when the original 10,75 mm cartridge was not available anymore.
the 10,75x63 is ultra rare today no doubt because it was so easy to rechamber such rifles to 10,75x68.
I believe that your rifle and the other Haenel too were once made for the 10,75x57! its simple to rechamber the 10,75x57 to the longer x68 case amd was made more than once
http://forums.nitroexpress.com/showflat.php?Cat=0&Number=206900&an=0&page=2#Post206900