Tim,
The 10.75x65R Collath is shown on page 72 in Dixon. The dimensions listed are: bullet diameter 10.56mm, case length 65.0mm, rim diameter 13.20mm, base diameter11.90mm, neck diameter 11.18mm. Cartridge listed from about 1900 to about 1905.
The discussion of this cartridge on page 73 says it appears to be a slightly necked version of the 11.2x65R Collath, which has the same dimensions as the 10.75, except the bullet diameter is 11.20mm, the case length is 64.85mm, and the neck diameter is 11.80mm. The 11.20 was available from about 1900 to about 1915. The discussion of the 11.2 on page 73 says it appears to be interchangeable with the 11.15x65R LK Express. If you check the rim recess and it indicates a significantly thicker rim than similar cartridges let me know and I will check another possibility.
Mike
