When we talk about "locked metal cabinets", what do we mean? Like an office cabinet (light weight) or something more substantial? That would obviously not be fireproof and in a house fire could perhaps put fire fighters at risk. Is fire-proofing not that important?
In my youth, I seldom had more than one carton of ammo at one time but the situation is considerably more complex now ( many calibers, many bullet types, etc).