He wants a load that shoots flatter at 500 yds., i'd say to use whatever load groups best at 100 and get one of new fangled tragectory compensating scopes! Or sight in for 300yds. or something. I'm not into this kind of thing but my 1867 made 38/55 hits dead on a 500yds. or any shorter range, as I just have to change the repeatable setting on my vernier tang sight. Surely the modern plastic rifle and TSX crowd has come up with something comparable!!