I believe the conditions of storage make a big difference, along with whether the ammo is actually loaded into a gun. Woe to the firefighter entering a place where there are many loaded guns. It appears the addition of the barrel creates a problem as it allows for the reduction of the area impacted by the explosion propelling the projectile. The shrapnel from the casing appears to be the worst issue, but it still could injure someone if it was not contained.
Here is the Mythbusters episode that Louis is talking about. However it does not mean a firefighter, or anyone else wants to enter a place on fire with ammo and guns inside if the shells are already going off!
But I still would not be happy about living near a person during a fire, who has many guns, lots of ammunition and brags about how he or she is prepared at any moment for a revolution, indicating that some, if not most of the guns, may be loaded.
I found out after a good friend died that his home and shop were filled with loaded guns hidden throughout. My shop was a few doors down.
We would have all been in danger with the weapons he had in our completely wood framed structure. Never knew things were that bad, he was a hoarder, eccentric, a loner, and used to have a gun shop.
I love you, old friend, but you really scared me in the end.
We were all so lucky we did not have a fire...