That looks like a nice powder magazine... the internal wood is naturally to make it static spark-proof. Typical magazine construction. You can do the same thing with any of the sheet-steel job-site toolboxes too. Makes a nice safe spot for everything. These are not designed to do anything but keep powder safe from tampering, and from static discharge ignition. They are specifically designed to NOT contain the blast from a powder ignition event. No sense making fragments out of a box that has become a pressure vessel. Powder in one and caps in another. No different than storing dynamite and blasting caps. Cap boxes can be made with a 20mm ammo can lined with wood, BTW... they work fine.
Glad to see you here, Clem... have a little project here that you inspired: Some .460 S&W brass, BP, and a Walker: Perfect Together. Need to send the cylinder out for reaming.