23.5 with 77's is what I use, best load to date. Your 1/9 will probably stabilize the 77, and almost definately stabilize the Hornady 75BTHP ( NOT AMAX) 1/9 AR's have troubles stabilizing, but most bolt guns do not, the extra speed and barrel length help.
24.2 H4895 with a 75 has been a great...