How about the 378 wby case? Then you could use the belt.
Or just shorten a bmg case to reduce capacity…..then you could use your existing brass
Thought of the 378 WBY case too. It would probably work. The 50 Spotter uses a shortened 50BMG case and would be legal but reloading anything 50 BMG related can be a pain in the butt, especially for a rifle that would basically be a fun toy.
375 Ruger is the NEW KING of the .375's. ALL HAIL THE NEW KING!