[Terriergal]

loose ammo is not a risk in a fire. The loaded guns were the projectile risk in a fire.

?

So... ammo in a gun is bad if heated up... but ammo in a box is not going to explode upon heating?

[Terriergal]

Maybe I'll have to try that experiment with my brick of .22 ammo...

[Tennessee_Bob]

but ammo in a box is not going to explode upon heating?

Don't know - we always considered munitions as a hazard during a fire. Then again, we were dealing with 20 and 30 millimeter ammunition - not exactly deerhunting rounds.

[Poohbah]

Ammo in the box will (supposedly) only go low-order detonation, not high order.

[Teacher317]

So... ammo in a gun is bad if heated up... but ammo in a box is not going to explode upon heating?

The gunpowder will still ignite, but the moment the slug leaves the jacket, all of the energy is released and little of it propels the bullet. If the round is in a gun, it is propelled with the full force of the chemical expansion, and all in one specific direction down the length of the barrel.

Compare the water calmly burbling out of your garden hose before and after you stick your thumb on the opening, either dispersing the force over a large area (the opening of the hose) or channelling it all in one direction.

[LibTeeth]

Smokeless powder is combustible, but requires containment for the progressive burning that makes it an effective propellant. It will detonate only under very specific and unlikely circumstances. In a fire, uncontained rounds will pop off their bullets with little force and burn out a little spurt. Black powder is a whole different animal, it burns rapidly at the same rate whether contained or not. It's possible to have black powder fixed ammunition. They would explode like firecrackers in a fire but the velocity of the freed bullet still would be much less than from a barrel.

Rounds in barrels in a fire will cook-off, where the pressure will build up due to the containment of the chamber and rifling retarding the bullet travel. The round will fire at full velocity. Fortunately, many powerful long guns are stored muzzle up in racks or safes, and pistol rounds are significantly less energetic.

[Godebert]

"So... ammo in a gun is bad if heated up...?"

If the round is chambered it has the potential to become a projectile. Rounds in a guns magazine will not become projectiles if over-heated.