One 'help' I've found with the .45 rifles and different loads that give only a vertical POI change,is to use a duplex-type crosshair with a low power scope, like a 2X Leuy. With the one load zero'd on the hairs at 25 yards, load zeros on the plex, either the top one or the bottom one. I also have this sort of arrangment set up on my 9.3x57 - the 285 Privi's zero at 200 yards on the bottom plex and the 232gr. Norma Vulcans zero on the hairs, same range.