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?
This topic comes up fairly frequently.
Ammo is actually far more dangerous in a fire when it's contained in a strongly-built and tightly-sealed container. This allows internal pressure to build up to extremely dangerous levels. The term commonly used for a strong and sealed container that contains gunpowder is a BOMB.
Uncontained ammo will "pop" harmlessly in a fire, like a July 4th firecracker. The flying bits of metal from the case and primer are only dangerous within a foot or two. The bullet actually won't travel as far as the other pieces because it's so much more massive.
The International Fire Code states that ammo and powder should be stored in ordinary wooden cabinets. Wood burns and won't contain much pressure, so the ammo inside won't cause a dangerous explosion.
The protective gear and face shields worn by firefighters are more than adequate to protect them from uncontained ammo fragments, even if the ammo were to ignite while the firefighter is standing right next to it. Ammo in a strong and sealed container
, on the other hand, may kill someone several feet away, even if he/she is standing on the other side of a wall from it.