Smokeless powder is not regulated as an explosive in the quantities used by reloaders.
The laws governing powder storage nationally...
There are no such laws in the US.
The SAAMI has RECOMENDATIONS as does the NFPA.
The recommendations need to be adopted by a state/municipality to have the force of law.
Just like plumbing codes, electric codes, building codes, etc. you have to look to your state (and possibly sub-municipalities).
Tha SAAMI wood 'magazine' is intended to allow easy removal of the powder in the event of a fire, delay heating of the powder if a fire is near the container, and provide a weak container that cannot contain pressure if the powder is ignited.
Smokeless powder will not explode if ignited.
Unless it is contained so tightly the pressure can rise as the powder burns it just fizzles and burns rapidly.
If it IS contained tightly enough to create pressure it makes a pressure bursting failure, still a far cry from an actual explosion with shock waves.