[bacondude3]

This is not true. 50 year old ammo will shoot indistinguishably from new ammo if both have been stored correctly. Prolonged exposure to water or high humidity can damage cartridges by preventing the powder from burning, but that doesn't make it more dangerous, only useless (at worst).

[Retric]

A large ammo stockpiles can make a house fire significantly more dangerous more so if you can’t depend on quick access to modern medical treatment.

Controlling humidity after a long term collapse is much more difficult. Less so in arid areas, but their hardly ideal without modern infrastructure.

[bacondude3]

Again, wrong. Ammo is not dangerous in a fire: https://www.youtube.com/watch?v=3SlOXowwC4c

As for humidity, I think you would be surprised. Much of Appalachia and the East Coast have high humidity levels (typically 70-90% during summer IIRC) and I've never found ammo damaged by humidity there. I've shot 25 year old ammo that was put in an ammo can and dumped in a hiding spot near a pond (so, very high humidity) and had no issues shooting with it. Even if the ammo is stored in the manufacturer's cardboard box, I wouldn't worry about humidity damage unless average levels are over 85 or 90%. Water damage is a different matter, but I don't have any experience with that.

[Retric]

That video is on Sporting Ammunition which is relatively low energy and shotgun shells which are reasonably safe in a fire. A rifle round cooking off is significantly more dangerous though without a barrel it’s below a normal handgun round, still the difference from that video is still shocking.

Edit: It's mostly true that ammo in a fire will just pop and maybe just throw a little brass a short distance.

BUT from that fire I'm witness to the fact that ammo can also "fire" with enough force to go through steel 50 cal ammo boxes and continue through such things as walls and cans. There were bullet holes through the shop's paneled and insulated tin walls. https://www.thehighroad.org/index.php?threads/ammo-in-a-fire...

I will admit I may be overstating the humidity issues, my personal experience was 15 year old ammo in Florida shed which had issues but clearly YMMV.

[bacondude3]

Do you have a source for that? I don't really understand why shotgun rounds would be less dangerous, particularly if rifle rounds are more dangerous. More powder = more dangerous would make sense to me, but that doesn't sound like what you're saying.

Some parts of Florida are more humid than Appalachia, so maybe the difference between 75% and 95% humidity has a greater effect than 55% to 75%.

[Retric]

I was told the rifle rounds where more dangerous, but not why. My suspicion is the plastic tube around a shotgun shell loses strength before the round is hot enough to go off ~200C. Though it’s probably more complicated.

As to humidity, I don’t know it might be just extreme humidity or it could be humidity + temperature, or perhaps we had a bad case of ammo to start with.