I'm following , I have the same question . Waiting on my seating die for the Berger bullets . But I found shooting 162ELDX bullets the R19 works better than the H4832SC , better grouping anyway . 57.5 was my best group , not sure about the FPS .
H4831 is really the gold standard powder for the 280AI. You will never go wrong with it. That being said, RL23 is just fantastic and my favorite to use in my 280AI. It's better than RL26, which seemed to always throw a flier for many of us that tried it