My experience 'over the course' and at 800 and 1000 yards was with a match prepped M14 with NM iron sights, and the old 'white box' NM 7.62 ammunition using the 'standard' 173 gr. boattail bullet.
The rifle and load are adequate at extended range, but there are better bullets and loads available now, notably with 175 gr. Sierra MK's. I thought for awhile that I was pretty hot "stuff", till I was introduced to a more experienced shooter and a Tubb bolt gun chambered to 6.5X284.....
With that M14 and load, I've shot several 'first round out of a cold barrel' X-ring hits at a thousand.
Doping the conditions out there are a LOT more important than the rifle and load, at least in my opinion, and the data I collected over time in my shooter's record book was invaluable for putting lead on iron way out there.