H322 is a great powder! It was designed to be equal to Thunderbird T-32, THE Powder for shoot Bench Rest with PPC and BR cases!

My bolt gun shoot a H322 load into tiny tiny groups! But is a few tenths over max for AR's

My suggestion would be; go to the Sierra and look at the load at the bottom of the section for that bullet, the accuracy load. Find the H322 line and go to that accuracy velocity and use that charge.

I don't believe that bullet has a cannelure, be sure to use a pretty stout taper crimp! COAL on all 223 AR's is 2.25" Max.

Ivan