I’ve fired an M-16 and A-4 many times with only iron sights, and had a fairly good grouping out to 400 yards. Not spectacular, but good.
This was while I was in the Air Force, not exactly known for grunt work. Imagine what a much better trained Marine or soldier could do.
Have grouped 1 inch out to 300 yards from bench with tuned in scope.
Great marksmanship on your part with iron sights.
If this guys equipment was tuned in he was very hasty in his timing and thankfully so.