This is from my maternal grandfather. Now, mind you, I'm 72+++ years old, so this goes back to when BP arms were the common arm.
Hold you hand out, palm up. Don't force you hand "stiff-flat" and don't cup it. Just relaxed flat.
Place the ball in your palm. Carefully pour powder over the ball until it is just
covered. Pick out the ball and pour the powder into your measure. Adjust your measure to just full. This is your standard load
for that ball.
Now, to work up the maximum load for that gun:
Lay a white sheet out in front of you. Shoot a round. Inspect the sheet. Then increase the load by about 5 grains volume. Shoot that round. Inspect the sheet. Repeat this until you see unburned
powder on the sheet. Decrease your load by 5 grains volume and call that your maximum load.
The hardest part of this task is getting that sheet past Grandma without her noticing how dirty it is.