This is another ‘Hollywood’ myth you probably have seen in a cowboy movie where in order to keep the bad guys at bay, the hero throws a bandolier or gun belt into a raging fire. Soon you hear rounds going off and bullets whizzing through the air with the bad guys running for cover. The hero escapes with the fair damsel and they ride off into the sunset.

Never going to happen if you understand basic physics and how a bullet is projected down a barrel of a gun. From my Gun Terms post:

Round

An ammunition round that has four basic physical components, a primer, a casing, gunpowder, and a bullet. A primer is attached at the one end of a casing and provides ignition to the gunpowder. The casing holds the gunpowder or propellant charge to be ignited when the firing pin strikes the primer, a bullet that is crimped at the other end of the casing, and is projected down the barrel by the expanding gas of the ignited gunpowder contained within the chamber of a firearm.

In order for the bullet to be ‘pushed’ out of the barrel, the gases have to be confined and pressurize before the bullet can reach a certain velocity and expel out the end of a barrel. Simple physics, ‘For every action there is an equal and opposite re-action‘. The gunpowder itself needs to reach approximately 427–464 °C before it ‘cooks’ off and ignites.

The video below is an excellent example of what happens when a round cooks off. Start at time stamp 12:20 for the fire tests.

Note: I usually let out a little whimper when they sacrifice all of those usable rounds of ammunition during the testing.

So if you hear of someone storing a quantity of ammunition and they have a house fire, the ammunition will not explode all at once, it will ‘cook off’ independently and each round will explode one by one and the bullets would not have enough velocity or a path to follow to be life threatening. I have not found any research for any issues of storing ammunition in a safe. This may have to do with different propellant charges reaching different ignition temperatures. I never seen a safe blow up from within before but I wouldn’t want to be the one to test this out.

There are instances where someone, for whatever reason, decided it was a good idea to leave a loaded gun in an oven. They turn on the oven to preheat it and, since a round is in the camber, the round cooked off and the resulting pressure shot the bullet out of the barrel. I think that the technical term for someone who does this is, ‘idiot’.

So if there is a fire near stored ammunition, I wouldn’t run up to it with a stick and a marshmallow on the end of it, but I would stand back at a reasonably safe distance and enjoy the show. You are more at risk with that can of gasoline you have stored in the garage for the mower or the back up tank of propane for the grill than you are with ammo in a fire.