I use an adjustable measure for testing loads in my rifles. When I find the adjustment that works, I 'throw' a bunch of those on the scale, weighing them to find
what the weight was, that works. I (record that weight for the rifle, patch and ball) then make a measure to throw that amount /weight of powder. I find if the
measure has a 3/8" inside diameter, I can throw charges with it, that vary no more than a couple tenths of a grain. The larger the diameter, the more variation
shot to shot there is in the weight thrown.
Tapping the side of the measure, then topping it off, as Pete noted, works well, but - you MUST do that the same each time or the thrown charge will vary.
Knowing and recording what that rifle likes, allows you to make a new measure to throw that weight of powder, if you lose the first one.