FYI- Yesterday I went and shoot my Model 70 in 375 H&H. I loaded the Nosler 260 gr. Accubonds with 67 to 71 gr. of R15 in one grain increments. Speeds ranged from 2620 to 2730 ft/sec. All loads grouped pretty good at 0.75 to 1.5. The best charge was the 70 grain going 2685 ft/sec and a .75� group @ 100 yards. Three of those 5 loads had 2 bullets in the same hole and the third bullet of the 3 round group out either .75� to 1.5�. The remaining two groups were clover-leaf shaped but 1.25 & 1.5�. All in all a good day at the range.

If you find you aren't getting the performance you want from RL15 you might try Varget...I've had a lot of sucess with it.

.375 H&H Magnum
Bullet: Sierra 300 Grain Spitzer Boat Tail
Powder: 78.7 grains of IMR-4350
Primer: Remington 9-1/2M Large Rifle Magnum
Case: Winchester
Firearm: Ruger #1
Velocity: 2596 FPS @ 15' from muzzle
Accuracy: 3-shot, 100-yard groups of <1"