If individual barrel groups are crossing it indicates too high velocity or too light a bullet. Increasing the velocity will only make the barrels cross more. Wade is going the right way, but it sounds like R15 is not for his rifle.

Each rifle seems to have its own preferences. For instance, my friend bought a Merkel .500 NE at the same time I did. We ordered them together. His rifle crosses with my load, and he was unable to find a suitable load with H4350. He found success with IMR4831.

Stick with the slower powders - H4350 or IMR4831. In my experience you will achieve better and safer results.

You only need one good load. Find it and stick with it.

Good luck,
Curl