I believe the fire standard is 1" wood cabinet or container if above 20lbs smokeless powder in residence.
The limit in most jurisdictions is 50 lbs. with the 1" wood.
I'm not sure about Black powder limits. I've read 10lbs. max several times. It's an explosive.
There is also a limit in most jurisdictions on primers; 10,000 max.
These limits are normally fire code. Be careful with your insurance as many have clauses saying you are not covered if you break fire code.
I built a wood powder box and have big ropes on it to pull out of the garage if time permits.
I store my primers outside in a dock box. I store my black powder in a separate dock box outside.
I always try to stay legal; who needs the hassle. My family's Safety is totally different; I take storage seriously, no matter what the system might say.
Prescut