What diameter are the bullets, and what diameter is your throat?
I won't comment on the powder charges other than to say they sound right in the ball park. The Lyman manual quotes a max of 27 grains 2400 with that bullet (2140fps), so it would seem you could ramp up the charges some more since you seem to be experiencing a trend toward better accuracy with each higher step in velocity.
My powder of choice for this work is 4759, but that's moot because it is no longer in production.
