QD mounts can hold zero, well within 1/2 MOA
Most QD mounts I've used and tested work well enough. 1/2 MOA group size variability is extreme and hard to attribute to the mount alone. Even the most consistent ammo can have 1/2 MOA variability in a vacuum. Environmental and user variables like wind, changing light condition, humidity and your blood sugar level can create more group size variability even if you had a permanent mount set-up. MOA by the way means minute of angle. 1 MOA = 1" @ 100 yds, 2" @ 200 yds, and so on.