Thank you kuduae,

I really appreciate your detailed information above. Thank you ever so much.

I have done a chamber cast, and there are no remnant tool marks in the neck area that would indicate rechambering from the shorter necked 10.75x63 caliber.

However, the rifling appears to start very abruptly at the case mouth, with little or no lead or freebore. I don't know if this would be typical for a 10.75x68 chambering, or if this would indicate a recut chamber from a shorter 10.75x57 earlier caliber.

I have some vintage 10.75x68 RWS factory ammunition, in both soft point and solids, which fit easily into the existing chamber with no signs of the chamber rifling touching the factory seated bullets.

So maybe this rifle was originally made in 10.75x68 and someone added the "10.75 X 68" marking to better identify the caliber.

It is nice to know that the rifle was made between 1912-1914.