This video from SAAMI (Sporting Arms and Ammunition Manufacturers Institute) was shot to demonstrate how much danger firefighters are exposed to when a fire includes stores of ammo. Conclusion: Ammo that “cooks off” due to a fire outside of a gun’s firing chamber presents little danger to firefighters. Normal turnout gear is sufficient to stop the low-velocity projectiles (bullets and casings) resulting from cooked off ammo.
Huge amounts of ammo were subjected to fire, impact, crushing and so on to see what happened. In the case where a round did go off due to impact, the effect did not propagate to other rounds.
If there are any loaded guns in the fire, the one round in the firing chamber will achieve close to normal velocity if cooked off. But that’s just one round.
Firefighters have less to fear from ammo cooking off than from normal fire hazards.
<http://www.pagegunclub.org/knowledge-base/>
This is my gun club’s web site and is new, lacking much information that is yet to come.