All of my past 3 .375 H&H as well as the 2 '06 Improveds, have put not only different bullet styles, but different weights into much the same group at 100 yards. They ran from 235's to 300gr. The 350gr. Barnes Originals struck a bit higher, just out of the group, but within 1-1/2" of the main 2" group. As for the rest, they'd make a 2" round group, 235, 250, 270, 285 and 300gr.
: The only way to find out if yours does the same is to shoot them.
: All books have good loading data. I tend to stay away from 4350 and such slow powders, but some folks like them. Appropriate ballistics can be achieved with less of the faster burning powders which also reduces recoil. About the slowest needed is Re#15. IMR 4064 has always been a great powder for me in my BRNO's, but doesn't deliver the highest velocities, just the best accuracy. Getting 100fps of velocity with an additional 10 gr. of slower powder isn't important, but great accuracy is.