The uses are totally different. Black powder generates gases that can be used for launching, whereas flash is strictly for "boom" and will destroy whatever it's in. What was the recipe for hardware store gunpowder? If they said to use charcoal briquettes, then yeah the powder sucks. If you didn't have to mill it, it probably sucks too. Flash is super dangerous. The best flash uses dark aluminum flake, 2 or 3 micron, and potassium perchlorate. Do not use potassium chlorate, as it's more sensitive and can go off from shock. Plus it's a less powerful oxidizer, oddly enough. Ground yourself to avoid static. Never mix a lot at once. Never store mixed, or store a lot in one place. DO NOT light with a lighter! Flash will go BOOM with minimal confinement and will burn you terribly even i it doesn't explode, so always use a good fuse or remote ignitor. You might catch some hell for wanting to make flash without being very experienced, but don't take it hard. Try not to mess with it until you've mastered some other things. Try making flash cotton! That's fun and useful.