I have an adjustable powder measure with gradations from 0 to 150. I am used to using a Tresco spout on a black powder cylindrical flask, these spouts being 15, 20, 25 grains, etc. These fill being threaded into the flask and holding your finger over it when you fill it from the flask and you fill your case. Let's say I set my adjustable measure to 40 grains. How do I fill it without getting black powder all over the place?