A "reduced" load that has worked for me in the .375H&H was: 41.5/SR4759/WLM/Win/225cast(sized). My records don't show the velocity of the load, but it was accurate, didn't "lead" my barrel, and was a "pleasant" load to shoot. The cast bullets I used were originally .379 bullets (38/55?) that I sized to .375. I found this "powder charge" in "Duponts data sheet" as a max load for a 270gr (jacketed) bullet at 53,000cup. It turned out, the same load, with a much lighter cast bullet, worked very well in my rifle without showing any problems with pressure (standard cautions apply, reduce initial charge at least by 10%!).
I particularly like SR4759 in many calibers, and for reduced loads, as well as cast loads. The powder is very "bulky" and precludes the requirement to use "fillers" in most cases.