Barnes published a recipe for working up loads, a long time ago.
Fred, I think it was, noted to load up from starting loads, 1 grain increments to a maximum load in a variety of powders suitable to the ctg. and bullet weight.
Fire each "group" of bullets at a separate target, THEN select the powder for that bullet weight by the smallest group spread. That way, you will have the smallest variation when using powders that vary with temperature and humidity. Of course, today, if using the modern non temperature sensitive powders, this is a moot point, somewhat, but an interesting and thought provoking concept.