I don't change the sights until I work out the load that I'm going to using, "most" of the time.
If the rifle is going to be used for deer hunting, then my personal limit is 50 yds. If I can get the ball or bullet, to try to give me a group that is acceptable to me. For example, one of my rifles is a TC Hawken flintlock, and I'm shooting a round ball, and after testing different ball diameters, patch thickness, 2F and 3F, and different lube combinations. I concluded that 70 grs. of Goex, with an .018 patch,.495 dia. ball and bore butter, was giving me the combination to shoot the group size, that I feel comfortable taking to the field to hunt deer with. It is at this point that I adjust the sights to point of aim. Of course if it was shooting way off, I would bring it in closer, then work from there. There is so many variables with a black powder rifle, that I feel you'd be chasing the sights all over the place, and with the move traditional sights, filing and drifting the sights would more than likely be required.
Seldom am I satisfied with the sights, that come on a rifle, and I am usally going to change from one style to another. I prefer, patridge style over buckhorn, and at age 62, only experimentation will tell,which is best.