thats so rare, I wasn't thinking to look for a rifle in this caliber. I believing that the existing rifles for the 10,75x63 where most times rechambered for the 10,75x68 after the war when only this cartridge was available and this must be a very simple job when you look on the cartridges.
do you have an original cartridge for the x63? last year I got an offer for an old 10,75x57 for 120 euro!
again Ernst Steigleder have the cartridge in his 1926 catalog together with the 10,75x57 and the 10,75x68, all three witht he 350 grains bullet. muzzle velocity goes from 620m/sec for the x57 over 650 m/sec for the x63 to 670 m/sec for the x68.
interesting to not are also the 10,75mm rimmed Gründig cartridges
10,75x45R G 575 m/sec
10,75x52R G 600 m/sec
10,75x60R G 650 m/sec
10,75x65R G 670 m/sec
again with the 350 grain softpoint
the barrel length is not mentioned

this here is the 300 grains speer, the first one I got. the speer have a little hollow base and its my general experience that such bullets will be more eays to resize than plan base softpoints. have also a homemade resizing die from .429 to .424.

can you recommand the 300 grains sierra as a hunting bullet on small game or is only some kind of a replacement?