For some reason you can shoot the same bullet at the same velosity, through the same gun and get 2 different points of impact. If I were tring to duplicate a factory load I would try to load several different powders to the factory velosity then choose the 1 that shoots closest to the point of impact of the factory loads with the same bullet the factory load uses.
Then another thing to consider is that if you just work up the most accurate load you can you might want to forget factory loads and stsrt shooting your own.
