We used to do it all the time on the farm. Purchased the sulfur ( called at that time flowers of sulfur ) at 10 or 20 pounds at a time. Made our own potassium nitrate, also made our own charcoal. The trick was to mix the ingredients wet and stir accordingly. Then spread the wet paste out on a sheet of plywood and allow it to nearly dry. Wet it again and this time grind it with a mortar and pestle. Let it dry. Do this as many times as necessary to get the mix you want and granular condition you want. We were told to never mortar and pestle dry black powder but I am sure we did small batches from time to time but this is not recommended. We would run off about a four or so pound batch at a time. It worked well and created lots of smoke when burning and made a dull bang when it went off. But, we used it blow beaver dams and tree roots. A fuse was made from icing sugar and potassium nitrate with a small amount of black powder wrapped tightly in news paper and soaked in egg glass and dried.