Why not keep powder in it? Anything I should know?
You really, really want to store powder in something weak, or that can vent.
gunpowder's burn rate is related to pressure.
that means no pressure = "burn" like "foom" Imagine a little pile you light with a match. That's why powder is sold in plastic containers, and they're designed to rupture at low pressure. It's also why the storage requirements for powder usually say something like "nominal 1 inch thick wood" .
But if you constrain it, the burn rate goes up, a *lot*. Like "boom"
You burn a pound of powder in an enclosed space, it might be a big mess, or it might make a bomb.
Burn enough powder that it's worth protecting (like maybe 10 lbs) and you're in deep do-doo if there's a fire hot enough to ignite it.