What applies to a bolt action rig, also applies to the auto rig as well.
In an AR, the barrel and bolt are treated to the same degree at the bolt action rifle, as well as the trigger, but the added mix is that the action has to cycle not only correctly, but consistently as well.
In a bolt action build rig, .3 MOA is about the norm, and with an AR match rig, .5 MOA is very tangible. Why the .2 difference between the rifle, it comes down to the mostly the chamber, and a tad on the feeding as well.
Now without writing a novel, you have to first tell use what type of rig you are looking at building (such as a CMP, or space gun rig), then we define it finer in there areas.