DP3 has it covered.
The only thing besides finding the right speed is I have a small hole in the straw and cut the mouth of the straw to be more castellated. I then turn the straw so the opening where the powder goes into becomes smaller or bigger according to the powder I'm dispensing.
Small opening for Ball powder, and bigger opening for stick powders.
Took me several months to find the right speed for everything so I only have to turn the straw and change it's opening to suite different powders.
Mouth of the straw... ( rough job I did at castellating it, but works great ).
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Different size powder inlet opening by pulling the straw out a couple of inches and turning it accordingly...
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My setting for speed with that size of inlet opening in the straw end up so only 1/3 rd of the opening is best for ball powders, and 5/8 to 3/4 of the inlet powder opening works for stick powder.
It makes the dispensing several seconds longer but way more accurate because once it's trickling it's able to throw 1 or 2 kernels of stick powder at a time ( castellated mouth of the straw has a lot to do with that as well ).