Looking old brass of 10.75x68 that a friend gave me I found two shells that were made it with 300 H&H.
Looking in the book of cartridge conversions they say nothing about doing it with that origin shell.
Now I am giving three shells to a machinist to see if getting out the belt and reducing the rim a little bit could be done .
Have anyone did this before?
Thank's

Well I post and answer my question .
I am really happy , with a 375 shell I made a 10.75x68 and it works perfect with full loads.
Sincerelly
Gtrotz