When you grind powder in a mortar you run the risk that your grinding pressure will produce enough heat to ignite the powder. If it's a squib amount it will startle you when that happens. If it's more it can spoil your whole day, set fire to your work area, cause injury and burns, and turn anything loose on your work surface into a projectile --- including the pestle you're using --- not to mention igniting the rest of the powder you probably left in an open container on the work surface. Under "cause injury" I personally have black powder grains imbedded in the skin of my face from being too close to a small charge that ignited, though mine was not by grinding. My glasses protected my eyesight. My recommendation is: DON'T DO IT!! T'AIN'T WORTH IT! IT CAN COST YOU MUCH, MUCH MORE THAN A CAN OF POWDER!
There floats my stick.
There floats my stick.