I use the larger of the three main bones in a turkey wing..., carve a wood plug to fit one end, then attach it. After that I take a brass adjustable measure, and using kosher salt as a substitute for real powder, pour the desired amount from the measure into the turkey wingbone measure. Light will pass through the bone, so holding it up to a light, I mark the outside of the measure with a pencil, dump the salt, and use a file to remove the excess bone down to the mark. Voila, a fixed measure. Then I pour salt into the new measure, and carefully pour this back into the adjustable one, to double check. Finally I do a test with actual powder to be sure. I have one for my .54 with its hunting load of 70 grains, and two for my .40; a 60 grain measure for deer (legal minimum in Maryland), and a 30 grain measure for targets and small game.
LD