If you can find it, WW760 will duplicate the factory loads and I have very good luck with it in my 375's. Ku-dude

With jacketed bullets I use VV N140.

RL-15 or RL-15 or possibly RL-15.
71 grains with a 300 grain bullet is all you need to know.

I agree with Vapodog, Varget is the way to go in the .375 I worked with the Barnes X 300 gr. bullets and tryed 4350, re-15, and finaly setteled on 69 gr. of varget with the new 300 Gr.Barnes Triple Shock for an honest 2510 F.P.S. chronographed on an Oehler 35P. Varget provides a load with about 99% density no more jumping up and down on the reloading press handle compressing those other powders