It depends on a lot of factors.
First is build quality. Do you have a tight fitting barrel extension to upper fit, or was it properly thermofit? Is the gas system dwell proper? Is it overgassed? Is it properly twisted? Is the barrel properly settled (same with a bolt gun). Second is the shooter. Do you have great fundamentals and a NPoA that is unaffected by the 4 recoil impulses (as opposed to one of the bolt gun). Third, do you have a good load that is matched to the twist rate and barrel length/gas system.
Most people get happy with 2 MOA from an AR pattern .308. Very few bother to, or even know how to, tune the variables for the best results (accuracy and precision) of a large pattern AR. Most of it is poor shooting fundamentals and over gassed systems. I'll be direct, I'm not happy until I can get under 1 MOA. Some of my Large frame ARs I just could not get better than 1 MOA, and some have dipped well below that. My current Large frame is STAG based, but neither upper, in 6.5CM and .308Win have Stag barrels because they won't deliver the accuracy I desire. They both produced 1 MOA out of the gate, before they were settled and without any specific load development.
What is interesting to me with these two current uppers is that every load throws the last round (at locking open) low and right, and I am still 1 MOA. When (and if) I get that fixed and tune a load, these have the potential to be under 1/2 MOA for sure.