@mfloski -- very hard question to anwer. We work with some very high precision brands, and in the 7.72mm NATO and 6.5mm CM, the best of the best rifles are going to give you around 0.75 MOA at 300 yards, and 1.0 to 1.4 MOA at 800 yards. 6.5 CM does a little better, generally as you punch further than 800 yards, over 7.62mm, but any gas gun is not going to give you the accuracy of a bolt gun, all other factors considered.
Keep in mind that the AR type platform was orginially designed for 2-3 MOA shooting by soldiers in the field, and that is good enough to hit a body at 400 yards or even further. With AR10/SR25/.308AR platforms, some manufacturers have build and sold sniper rifles to the military, like LMT and Knights Armament, and others have worked hard to build a precision rifle like JP and LWRC and others.
Like any gun, the accuracy starts with the barrel, and then moves to the opic, and then to the frame and bolt, so you will find quite a variety of quality in all areas. And then, you get to dimishing returns and spending a lot of money.
But, you know this...