Although it doesn't directly apply to the .375 H&H (and maybe not your source of load data), the H4895 loads I've used in Hornady's manual have always been too hot for the rifles I was loading for and I got the same symptoms you describe. I have an unused pound canister because I couldn't get loads I was happy with using that powder even when I reduced way below the starting loads.

It's limited information, and I'm sure there are good H4895 loads around, but thought I'd pass it along anyway.