It kinda surprises me that people are having such knee-jerk reactions to the idea of running a couple ounces of charcoal & sulfur in a ball mill. I took a spoonful of ball-milled charcoal/sulfur mix and tried to ignite it with an open flame. Not very exciting. It smoldered & smoked a little where the flame hit it. Smelled like sulfur.
Hey, guess what, it's not blackpowder without the potassium nitrate!
In the few weeks I've been experimenting with it, I've tried three different preparation methods. Some are better than others. I chronographed a couple of shots with each batch, comparing them to Goex 3Fg. The best homemade powder was right up there with the Goex, on a "weight" basis (eg, 20 gr of homemade vs. 20 gr of Goex).
The biggest difference I can see is that the homemade powder is less dense than the Goex. A powder measure designed for 40 gr of factory BP will only throw 30 gr of the homebrew stuff. In firearms like percussion revolvers and breechloading rifles (eg, Sharps, Smith) where chamber volumes are constrained, the reduced density of homemade BP might be an issue.... in this respect, I would agree that factory-made powder is superior.... however, I can still pour 30 gr of homebrew into the chamber of my Uberti .44 Remington's cylinder, and the "fluffy" homebrew powder compresses easily.
I don't know anything about loading blackpowder into rocket engines. It sounds like it might be a lot more complex than firearms powder. Just for the record, the last blackpowder I purchased from Graf & Sons came packaged in plastic containers.