I've only loaded for three .280's, but in all three H4831 worked better with all weights than either IMR4350 or H4350. (In one rifle RL-19 was the most accurate powder, though not by much over H4831.)

Have also had better luck with H4831 than either IMR or H4350 in two .280 AI's.

“Montana seems to me to be what a small boy would think Texas is like from hearing Texans.”
John Steinbeck