There is that "danger to self/others" criteria that the Men In White Coats have operated under for a few centuries...

The thing with black powder is that it, in sufficient quantity (5 lb+), constitutes a "magazine" which not only has to be stored in a separate and secure structure such as a reinforced concrete bunker with a steel, bolted and locked door, warning signs, and be so many feet (50 Rods) away from other buildings, mine shafts, daycares, etc. It's one of those "Duh!" laws if you really think about it.

It's actually illegal to use Black Powder for blasting purposes in WA because it's so volatile and unpredictable.

Don't ask me how I know this.