I checked my notes and the 350 gr. .416 Rem loads I did were with 4064, not 4320. But, I have both.
Like Jorge said, those big bores are pretty forgiving. A number of mid range powders will work
Barnes shows the 400 gr accuracy load with A-2520. Don't have that one, but it's on the same burn rate line as IMR-4895 and Varget.
I'll figure out something.
DF
