..from another board
.small arms ammunition will cook off due to heat. Due to high heat the powder will ignite and burn, it does not explode. Ammo stored in boxes will cook off, with the bullet and cartridge case seperating....the bullet does not move very far, but the brass case may. Sometimes the brass case will fragment.
If the ammo is stored in an ammo can, the gaskets have usually started to melt also...the ammo will just cook off in the can, with the gaskets venting the pressure.
If you pour a canister grade smokeless powder on the ground and ignite it.....it burns.
The same things happens to a loaded cartridge when exposed to heat.
If the round is chambered...we now have a different situation. Since the pressure is contained in the chamber....we have a similar situation as if you fired the round. Not good.
And, we all know black powder behaves much differently, not the same a smokeless powder.
I have been in several structure fires involving ammunition and reloading components. The rounds will cook off....with pieces flying about. I have had brass 357 cases bounce off my SCBA facepiece and turnout gear. It does get your attention, but is of no danger, if you are wearing your equipment properly. It does makes for some interesting feedback from the neighbors.....they hear the rounds going off and are yelling at you as you make entry in the structure!