Well that's a puzzler Blackelk, given that you say it's doing it with a variety of loads. If your load is anywhere around 70 grains or more, I just don't see how a gun that shoots a reasonable group sighted in at 100 yards can be that high at 50 with the same load and sight adjustment.

I can't think of a solution, or even a place to start checking. Does it do the same thing with bullets other than maxis? Ordinarily I would suspect you are taking a different sight picture at the two different ranges, but the peep/globe sight arrangement should pretty much eliminate that. Still, you could try having someone else shoot it to see if they get the same results.