Hi: Just treat the big belted case like you would a regular rimless case. You can F.L. resize for trouble free hunting ammo , partial F.L. resize for your rifle alone so the shoulder is not being set back , thus getting longer case life , or neck size only your own fired cases.
It's not any different I found than another case...
Also I used to crimp , but no longer do , accuracy will improve right away if you don't.
If you shoot for practice in hot weather , you can use standard primers. My hunting ammo in cold weather gets mag primers tho.
As for powder , the big 375 can use a wide variety. I have used IMR's 3031 , 4064 and 4350. Also H4895 and 4350.
My best accuray was with H4350 and Hornady 270 gr R.N. bullets from a Win M70 (post-64)
Watch your O.A.L. as I found out I could seat the bullets way out - but would not function through the magazine , have to compromise on that one.
Let us know how you made out. More questions? Ask away...
Regards,
Bob