Measure the pyrodex by volume, same as the blackpowder charge.
I use neat windscreenwasher fluid to clean my smoothbore musket. With the barrel off and the nipple out and the breech end immersed in washer fluid I pump it up and down the barrel with a patch on a cleaning rod, then dry with a paper towel on the rod. This gets it very clean and the washer fluid evaporates quickly.
Daz