I have used 7.5 grains of AA #5 in a 223, for 1800 FPS. Makes a sort of super 22 Mag round.
It's not directly responsive to your question, but I'd want to be sure that I used something that lights easily and uniformly. I don't know how Unique is in that sense, but TiteGroup does claim to overcome the problems often associated with small charges rattling around loose in the case.
