Sanding the end grain a couple of grits or more past the rest helps some. I also like to tint the finish, that seems to help level out minor differences. A little difference on end grain is OK in my opinion (not worth much) on most places, as it reads a little like a shadow line and gives the feature more definition, e.g. on the lock panels, but I know you want to minimize the differences, especially in some areas: On some stocks, the wrist can be a big problem, although long rifles tend to minimize the issues compared to modern stocks, with their pistol grips and usually uncapped fore ends,etc..