I can barely tell the difference between a ,223 chamber and a .223 Wylde chamber shooting for precision. With match grade ammo, both of those chamberings should produce sub-MOA groups to 300 yards at least provided all else is proper. Most of mine, benched with high magnification glass and match ammo, are in the .3 to .6 MOA range at 100 yards
With a 5.56 chambering and match grade ammo I have rarely been able to get better than 1 MOA at 100 yards with most in the 1.5 to 2 MOA range with match grade ammo. 69 grain Nosler match does produce 1.1" 100 yards groups from my 16" Del-Ton barrel, but that is an anomaly.
When I put a Red dot on, my groups tripple, at 4x they almost double. I need 10X to wring out the best accuracy and I only have a few AR15s with that much magnification.
Based on my observations at the range, hunting, training, etc. The shooter who can consistently hold 1MOA is rare. If you have a 1/2 minute rifle and shoot into 1.5MOA, well 1 minute is you. If you hold 1.5 minute and shoot a rifle capable of 1.5MOA, you end up with groups around 3 MOA, which is pretty common. Go to a .223 or Wylde chambering, that would give you maybe a 2MOA group.
With a bolt gun, everything perfect (low pulse, rested with a loaded bi-pod, rear bag no wind 20x on the optic), my contribution to the group size at 100 yards is just over 1/10th of an inch. With an AR15, my contribution is just under 1/4". I have shot smaller groups, but I also know they are not repeatable over time.