How to Store Ammo Without Ruining It

After the pandemic-fueled ammo shortages of the past few years, law-abiding gun owners know that having some ammunition on hand for the dry times isn’t a sign of paranoia or sociopathy. However you define “stockpile,” it’s smart to maintain a good supply of ammo–whether you hunt, shoot competitively, or just enjoy a day at the range with friends.

The problem is, ammunition has an expiration date. Its metallic and chemical components break down over time, and that degradation can render the ammunition useless–or, more concerning, dangerous.

Whether you have 50 or 5,000 rounds stowed away for a rainy day, how do you make sure they’ll last long enough to be used when you need them? Keep reading to find out.

Heat, Humidity, and You

To help me answer this question, I reached out to Sean McGee, the Vice President of Operations for Sig Sauer’s ammunition department. McGee said that under ideal conditions, ammunition can last as long as 20 years. Unfortunately, many gun owners fail to keep that ammo in those ideal conditions.

First, McGee encourages gun owners to keep ammo in its original packaging. It can be more space-efficient to dump loose rounds in an ammo can, but that destroys the information about the lot and date of manufacture. Even if you store ammunition in a climate-controlled environment, you won’t know when 20 years are up if you don’t know when this or that round was manufactured. (It’s also worth noting that the date of manufacture is different from the date of purchase.)

According to McGee, the most common mistake gun owners make is storing ammunition in hot or humid conditions. Heat and humidity are two of the biggest threats to well-functioning ammo, so it’s important to keep it in a cool, dry place.

“Powder has a limited number of high heat cycles that it can endure before chemical decomposition begins,” he explained. “Every exposure over 120° F has a cumulative effect and accelerates chemical decomposition of powder. If you have a habit of throwing a box of ammo in the front window of your pickup, replace it every year.”

Cars can reach 120° after just 40 minutes on an 84° day, according to the National Weather Service. If you keep a loaded firearm in your car, you should replace the rounds in those magazines at least once a year.

Attics are also a bad place to store ammo. Depending on where you live, attics can easily heat up beyond 120°, and unventilated attics can hit 170°. Even if you store your ammunition in sealed containers, those rounds will still get too hot if they’re left in these environments.

Humidity can impact virtually every ammunition component except the bullet.

“Humidity causes surface oxidation, which over enough time can compromise case integrity,” McGee said. “Long-term exposure to high humidity can also cause deterioration of primer and powder performance.”

You know you’re storing ammunition in a too-humid environment if you start to see green oxidation on the case. Also called verdigris, this is the same process that causes rust on iron. It happens when the brass case is exposed to an oxidation agent, usually the oxygen in water.

It could also be due to exposure to chemical agents. McGee discourages gun owners from storing ammunition in the same container as bore cleaners and other cleaning agents or anything that contains or releases ammonia.

“Exposure to ammonia is a killer for ammunition. Never allow cleaning agents or animals near stored ammunition,” he said.

A little green on a case doesn’t mean the ammo is worthless or dangerous, and it can be polished off if it bothers you. However, excessive green oxidation is “always a bad sign,” McGee said. It can indicate a deterioration of the case, which can be very dangerous.

“Case separation or splitting, unpredictable pressure, hang-fire, and squibs can all occur. Each one of those failures can lead to dangerous situations,” McGee said.

If in doubt, the safest bet is to get rid of the ammo by taking it to an approved disposal site. In many towns and cities, this is the local police station, but some landfills, gun stores, and gun ranges also offer ammunition disposal services. Searching “ammunition disposal” and then the name of your town and state on the Google machine should send you in the right direction.

Storage Solutions

Of course, no one wants to throw away ammunition, especially at these prices. The best ammunition storage solution is also the simplest: keep it in its original packaging and in a cool, dry place.

For most of us, that means inside the house. Central air conditioning systems keep homes cool and dry, which means ammo can be stored in boxes in a closet. If you’re concerned about security, those boxes can be stacked in a locked cabinet or safe.

If you (or your significant other) would prefer not to store ammo inside, the solution gets a bit more complicated. Garages, workshops, and basements are common places to store ammo, but you’ll need to jump through more hoops to make sure it stays relatively cool and dry.

How hot the ammo gets depends on where you live. Most regions in the U.S. don’t reach 120° outside, but a poorly ventilated shed or garage can get nearly as hot as an attic. If you’re unsure, use a thermometer to check the temperature of wherever you want to store ammo on a hot day.

Humidity also depends on where you live, but you can do more to mitigate its impact. McGee recommends military ammo cans for ammunition storage in part because they offer protection against humidity.

“Military ammo cans have been time proven and tested and offer excellent protection if the integrity of the can and seal are good,” he said.

As an added precaution, you can add silica gel desiccant packs or rechargeable mini dehumidifiers. Combined with a good seal, these will ensure that even if the cartridges get a little warm, they’ll stay dry (just be sure to replace the desiccant packs about every year, depending on how humid the environment is).

Last Shot

Ammunition, much like firearms, is an investment: not necessarily a financial investment, but an investment in convenience, camaraderie, and enjoyment.

Having your favorite hunting rounds on hand means you won’t have to scramble to find them before next hunting season rolls around. Collecting handgun ammunition lets you invite new gun owners to the range without making them purchase their own ammo, and having plenty of practice ammo means you can keep shooting during the next shortage (there’s a presidential election coming up, after all).

The point is, you don’t have to be a wild-eyed prepper to keep a supply of ammunition in your home, basement, or garage–and keep it in good working order. If you like to hunt or shoot, it’s really just common sense.