Shooting at something small, say a soda can, at 500 yards with open sights is beyond my ability. Yours, too?
I need to see the target. The "bullseye" on a 600 yard prone highpower target is what, about 30 inches across? I guess this is a corollary to the sight picture. The front sight post about covers the bullseye at 600, so be realistic about the target.
Lee