Stock fit? That's why some manufacturers provide stock shims. So the shooter can adjust the point of impact to where he looks. And, some guns are just a little out of whack. Once I was assigned an 870 for my patrol car. Knowing how fickle shotguns can be I took it to the range before hitting the street with it. Buckshot was identical to what you described, high, really high. A slug at 50 yards was about 3' high! I exchanged it for another identical 870 from the rack in the armoury, and, guess what? Shot perfectly to point of impact!