1800 rounds in a 223 is not many at all. If i read your first post right you changed rings and scope and then your groups opened up. It could be a parallax problem, that would sure account for the group opening up. It could be the lot of bullets you just got or maybe you started on a different lot of powder. Seating depth changed (bullet lot again), throat moved a few thousandths (seating depth again). 223 barrel should be good for anywhere from 4000 rounds to excess of 10,000 but i would look for 4-6000 as the change barrel place.