well, this is confusing

the only proof load I found for the 10,75x68 was the one with 3,7 grammm what makes sense with 3,5 gramm for the x63 an 3,2 gramm for the x61. now you have an original 10,73x63 that was proofed for 3,8 Gramm Gewehr Blättchen powder. the only catalog data I ever found for the 10,75x63 was in the 1926/27 Ernst Steigleder catalog:

funnily enough with exakt 3,8 gramm Rottweil R5 powder that was given less power and pressure than Gewehr Blättchen powder, obviously. Why did they use the military rifle powder pre WW 1?
probably because it was made to the highest standard and greatest equality when nitro powder were showing more variations from lot to lot than today.