My 75gr hpbt hornady bullets would not group?
Why are you using Bolt Action bullets for an AR? Are you shooting then one at a time, if you are using the correct OAL for this bullet it WILL NOT fit in your mags.
I get excellent resuts with these bullets, but out of a bolt action Savage Model 10 with a 1:9 twist. If loaded to the correct OAL your AR will be a single shot rifle.