The only way I can see this being a problem is if there is slop between the upper and lower causeing the upper to move different with each shot. This is a very common problem with the M-16A2's I was issued in the Corps. Most of these rifles were better than a decade old and had been fired tens of thousands of time and had the crap beat out of them. My last M-16 had enough slop that the muzzle could move 1/4" in any direction with the lower fixed. Not the most accurate rifle, either.
New commercial AR's are going to be much tighter than a rode hard and put away wet M-16, and if there is any slop, they make a little wedge shim that goes under the buffer to tighten things up. There are also adjustable action pins that will do the same thing available. You probably won't need them, though.
Mike