In the most recent batch of 2nd hand reloading gear I purchased there was a 1971 edition of "Handloading" and contained therein was a really interesting study on the accuracy of dippers. The author advocated making custom dippers but for his test he used the Lee dippers of the day. These were assigned random numbers back then -not the cubic centimeter volumes of today- so I can't tell you the exact grain weights they were tossing, but they did list the variances they obtained weighing 10 charges from several dippers of various sizes, using a half dozen different kinds of powder. The results were impressive.
The finer powders all hit .2 grains max run out. Most were .1 grain. The coarse powders -H4831 and IMR 4350- did poorly with the smallest dippers (.9 gr variance for H4831) but in the larger dippers also stayed in the .1 and .2 grain range for deviation. This is as good as many of the best commercial powder measures.
The author emphasized technique: He used a large volume of powder and pushed the dipper base first into the powder, letting it fall into the cavity. When submerged in powder he raised it up and out of the powder and struck off the excess with a small pocket knife blade or card. The technique of pushing base first is recommended by Lee and is why they call the dippers, "dippers" and not "scoops". You dip the unit into the powder. You don't 'scoop' up the powder with the dipper.
I was bone tired when I read the article but that was the bottom line: That dippers aren't to be scoffed at when used correctly.~Muir