Also, look up the process of "corning". Necessary for bp.

Hold this thought, too. Most BP mills in the early days were built very flimsily. So when the mixture went up, the burn wasn't constricted. No iron tools, usually wood. How are you at wet grinding to uniform size?

Yeah, it's sulphur, charcoal and saltpeter, but that's only a vague start.

Much easier to buy the stuff.