Re: Screw on or AAC quick attach?
My burgeoning experience here is that a good QD system will return to zero. My 7.62SD 51T suppressor threads on and locks into the same tooth every time--which is no surprise considering that the can threads onto acme threads and must lock up onto the mount shoulder at the same point before it hits that last tooth on the latch. In other words, the can is being torqued to the same point every time, and you are assured of reliable POI shift.
My results on my AR10 are showing .6 mils low at 100 yards, every time. Groups tighten from ~.75" to less than .5".
I can see how a QD system might introduce some variables that would affect accuracy--bad thread concentricity which stacks up when you add in a mount, bad mount to suppressor contact, the suppressor not torquing down the same each time, etc., which might make the thread on can simpler to make repeatable.
However, when done correctly, a QD suppressor can be just as accurate as a thread on can, with the bonus that, with a latch anyway, the can will not back off.