You may want to try AA2230 or H335. I have been shooting the 6mm-223 for over 17 years and found these two powders to give higher velocities than the H322.
But on the other hand, I have not found a powder more accurate than H322 in this round.
NOrmally, groups open up by about 1/2 inch using 335 and 2230 more than using H322, at least in my 14" contender. Groups go from about 1/4 to 1/2 inch groups to 3/4-1" at 100 yds.
It's not a rifle, but I have used this round quite a bit and thought I would provide you my .02 on the powders I have found successful.
Good LUck, it's a great round for anything up to Mulies with 80gr. bullets.
HL