Hitting the sweet spot requires 1/10th grain measurements. Usually doesn't show up in straight wall cases as much as bottle necks.
You can divide the velocity by the grains of your load and come up with approx. Fps per Grain. I use Algebra all the time to figure
out equivalent loads from one powder to another if not available in manuals. To do this you have to have some knowledge of burn
rate and types of powder. I use this to reach basis for starting loads. I don't have any fancy CUP instruments, but I have a brother
that will shoot anything. If he comes back with all his parts I know it's a good load.