I made a weak BP many years ago. I didn't know what I was doing. It would burn but not really explode. I have since then (the internet days) learned much more about it. It is not as simple as it seems. Yes you can make powder but I don't think you can match the commercial powders. I am reading the Cap Lock Rifle Book right now and different powders are discussed. And cussed. Some burn cleaner with more strength. Some are moist after firing and clean easily. Others do not. This was in the heyday of BP shooting.
I did buy 10 pounds of pure Potassium Nitrate from the link below to make my own powder. Also the gunslingergulch link will show you how to make powder and where to buy a tool to compress the powder to a puck so you can corn it in a grinder. The same guy that sells the tool will also sell you charcoal.
After all the research and watching videos I decided it is just better and easier to buy the powder and primers. I had a Tap-A-Cap tool but never got it to set off a rifle. So now I have around 40 pounds of powder, Goex, Pyrodex and Alliant MZ plus 8000+ caps. I am good for now. And I really liked the MZ powder. If you buy powder get the 25 pound lot from Powderinc. No hazmat that way. Get a bud or two to split the order with you. Thats what I did.
http://gunslingersgulch.com/index.php
https://www.seedranch.com/shoppingcart.asp?Check=True