“Lord Kalvan of Otherwhen) is a good go-back-in-time story by H. Beam Piper. It’s fiction but he put a lot of thought into introducing new tech, gunpowder in particular. The “bad guys” were not using an optimum formula for their powder, Calvin had a better way and it shot better, harder, faster. So the bad guys spread the word that THEIR powder was expunged of evil spirits- but Calvin’s powder was not, and anyone using it was doomed to an unpleasant afterlife! The novel was originally called Gunpowder God
We got pretty precise with out black powder formula. My Dad made a balance scale with a sealed bearing and some metal rod. Once we got the ratios by weight (don't recall right now) we measured out aluminum foil and cut it ito 3 pieces by x-amount of square inches to use as the counter weights. We would put it in a tobacco can that was brazed to a fitting that allowed us to attach it to a motor held in the vise to do a some slow turning and let the homemade .45 slugs we put in it do the grinding process. When ready to test, we would put a small amount out and light it to see how it burned and check the residue. then we could fine tune it by adding what was needed to get the most complete burn. If we wanted a real fast burn, we would use a putty knife and a Masonite board to work the required amount into a talcum powder fineness - get a match any where near it and it would just go poof - made some nice cherry-bomb type devices with the real fine stuff....By mixture and how fine/coarse you made it, you could make it burn anywhere from instantaneous to a slow fuse fizzle.