Many preppers have an small arms ammunition storage area in their preps. This seems to give some people heartburn and they complain about its dangers. I spent many years as a fireman and an arson and bomb investigator. During this time I attended many schools on the hazards of explosives and chemicals. I have seen the results of ammunition burning on many occasions. But I have never seen it cause a problem.
When ammunition burns in a fire unless it is in the chamber of a weapon, since it is not contained, the case ruptures and it only travels a short distance. Even if you are close to it will not develop enough velocity to hurt you.
Ammunition storage really only has three main enemies, they are heat, moisture, and chemicals.
Over time excessive heat will break down both the primer compound and the powder. This can lead to unreliable ignition and less-than-optimum velocities. According to Rick Patterson, Managing Director of SAAMI, “In fact as long as your ammunition is stored at normal room temperatures with low humidity, it can function reliably for decades.”
SAAMI believes the breakdown begins around 150 degrees Fahrenheit. There are very few environments where stored ammo can reach those extremes, however the trunk of your vehicle is one of them. “Definitely avoid storing ammunition in a car on a hot sunny day—that’s probably the single most likely scenario that could cause problems for the average shooter,”
While cold won’t normally affect ammunition, it could create storage conditions that expose your ammo to moisture as a result of condensation from extreme temperature changes. Moisture will lead to corrosion of the cartridge casings. This can cause failures to feed or case failure.
Chemicals such as organic solvents, ammonia, paint thinner, cleaners, and oils can penetrate the casings, damaging any ammunition which hasn’t been properly sealed particularly around the primers. Ammo that has been exposed to chemicals may not function reliably.
Just keep your ammunition storage where it is room temperature, dry and protected from chemicals and it will last for decades.