A9 is one of my go to 10mm powders. 12.5gr under a 200gr Gold Dot will give me 1340fps, SDs in the single digits, low single digits and fantastical accuracy, and that's why I buy lots of it. I have loaded some 44 mag stuff with it and it performed fine but not like it does in the 10mm. 1343fpf, 7fps ES and 3fps SD with a 2.2" 8 shot group at 20yds is pretty fine in my book.
2400 I am completely unfamiliar with sadly. I have found that many of the oldies are still goodies, I just cant ever find any Alliant powders in stock anywhere. Must be a reason for that.