Way back nearly 60 years ago a few other guys and I decided that making black powder would be fun. We knew what we needed and trundled over to the nearby Rexall drugstore to buy sulfur, potassium nitrate, and made our own charcoal (only the best for us!). Since we didn't really know how it was supposed to be made except for the proportions all we usually got was some stuff that stunk like sin when it burned. Now if we'd added a little water and mixed it up well, then dried it and broke it into powder we might have had an explosion and even more trouble from our folks than we got.
This is the first I ever heard of using magnesium in "gun powder" though. The guy's lucky he didn't hurt himself seriously.
Black powder isn't dangerous unless you've got a fair amount of it - a pound or so = and feel a need to make sparks, smoke, or something similar. I've had enough stuff go bang in the lab that this stuff has sort of lost it's thrill.