I have a friend going through the same problem with a high dollar .223 Remington. He had found two factory loads that suited him and shot only these loads. his competition load was Black Hills reloads in 75 grain, and his practice load was some Ultramax cheapies. You can't buy Black Hills 77 gr. reloads now (there's a war going on you know), so he's going through a wicked learning curve on precision reloading. In his case, we know it's the ammo and he hasn't found the right combination yet for his rifle. His 3/8 MOA rifle went straight to 7/8 & worse.
Back to your situation, have you tried your ammo in other rifles of known accuracy to see how the ammo performs elsewhere? My ARs all seem to have different preferences, maybe you haven't found a load that your rifle likes.
