The reason that you see unburned grains of 2400 is that it's 2400 (G). Sorry about that (VBG)! No seriously, 2400 just plain doesn't burn cleanly, not 100%. I've been using it since the '60s in lots of loads for lots of calibers, still got maybe a pound of my last caddy left, time to order some more. It's a wonderful powder but it WILL leave lots of unburned grains even with the heaviest loads.
Regards, Joe

You can lead a man to logic but you can't make him think. NRA Life since 1976. God bless America!