I have found it to be a common happening with heavy for caliber bullets. Even had 300 yard groups SMALLER than 100 yard groups. Truth be told, with a .338 Lapua, i wouldn't even look at accuracy until I hit 600 yards, and that would just be gee-whiz. I'd set my loads for 1500 yard groups.

Yes, what load you use can vary greatly by the yardage being shot. Quite often the best 100 yard group is not going to be the best 300 yard group. And the best 300 yard is not always the best at 600 yards. Get the distance you want to shoot at and work your loads for that distance.