IMR-7828 would be my starting point. I found RS magnum to be spikey (another techy word) in my current .264. This baffled me since it is such a slow burner in most cartridges. 7828 came to pressure gradually with no surprises. Accuracy was good with both.
I worked up to 65.5 7828SSC this weekend with the 140 Accubond. Velocity was just over 3200fps, accuracy was sub MOA.
