If I am bench rest shooting on bags using a basic m4 type ar15 with a 1:9 16" barrel, I expect 1 moa out to 300 yards with a 3-9x Nikon scope and adequate 55 grain ammo.

Having said that with a 20" 1:8 stainless barell and competition trigger and match ammo, you should expect sub moa easily.

The cheaper the ammo the larger the group. This is true of all firearms.