The 7.62 AR platform is going to be accurate, DI or piston. The $1200 DPMS can shot as well as the $10K KAC, it's just not as pretty
The AR platform is accurate in general, but a $1200 LR308 just won't be at the same level as a $4.5K KAC SR-25 because the overall fit of the KAC is better, it has a match barrel, and a great trigger. A $2500 P308 is more accurate than a KAC SR-25 because of the upper receiver design, believe it or not. The upper receiver on both the Larue OBR and P308 is thicker making them more accurate. The SR-25 is way overpriced.
I can get about 1.25 MOA out of a LR308.