On the ammo storage side of things, the important aspects of weather are the swings in extreme temperatures and how heat accelerates oxidization. Extreme temperature changes, especially when those changes occur over a short period of time, will affect the expansion of the various components. Let’s take a look at some best practices for storing firearms and ammo in warm-weather months.
Some General Rules
Brass has a different expansion rate than copper, lead, or steel. This difference can affect the seal between the brass and the projectile, or the brass and the primer. Loosening these seals may allow fresh oxygen and moisture into the cartridge. The fresh oxygen accelerates the oxidization process (read as slow burning). In effect, this will decrease the energy delivered when the round is fired.
The addition of moisture can be a bit more problematic. This can greatly reduce the percentage of burnable powder (wet powder doesn’t burn well) or cause the granules to clump. Clumping will change the shape and burn rate of the powder as well. It may even (rarely) cause detonation.
Please realize, this is not a process that happens (assuming quality ammo) when you leave your carry gun in the console once on a hot workday. Although the interior of the car may well hit 140-150 degrees, this is a process that takes numerous large temperature swings over a significant period of time. Having said that, if you routinely do this with your carry gun, it may well be time to replace what’s in the mag with some fresh ammo and use the old stuff for practice.
The Warm Weather Effect
I never have carry ammo in the gun for longer than six months. Just like replacing optic batteries, it is cheap insurance. This is much less of a concern for your bulk ammunition that is stored inside the house. Most of us keep the house between 68-78 degrees all year long. That is not even close to an extreme change. With that mild of a swing, you may see effects in 40–100 years. Those of us who keep cases of ammo out in the non-climate-controlled garage are a bit more likely to see these effects over a course of five to 10 years.
We recently had a day in Tennessee where the low was 29 degrees and the high was 87 degrees. My garage probably only dropped to 35, but in the heat of the day, it got well over 100 degrees. That is a pretty big swing over an 8–10-hour period. Having this happen dozens of times during the year, plus having 30–90 days where the garage temperature exceeds 100 degrees, is not good for your ammo. Remember, the high heat accelerates oxidation, even without adding more oxygen.
Addressing Issues
Here are some ways to mitigate ammo storage issues:
- Don’t store your long-term storage ammo in a place that is not climate-controlled.
- Rotate your practice ammo so it never sits for more than three to five years.
- Rotate carry ammo over to practice ammo status at a minimum of every 12 months. Six months, if you are often heat-abusive to the ammo.
People are going to hit me in the comments regarding spam cans, self-sealed ammo cans with oxygen absorbers, or vacuum-sealed ammo bags. All of those things will help to keep out moisture and the corrosion associated with it. It does not affect how heat oxidizes propellants or how those same cycles can loosen uncrimped ammo and primers.
I will also get comments regarding the surplus Russian 7.62×54 ammo that is ’45 vintage and got dug up from a field outside of Kursk back in the late ’80s, that shoots great. That ammo was in spam cans that were buried. Do not underestimate the insulation value of a couple of feet of soil. Second, you are not seeing the percentage of spam cans that were too ruined to sell. Thirdly, I own several Mosin’s and only one will shoot groups better than four inches at 100 yards, some shoot eight inches. How are you going to notice deterioration with that lack of precision?
Some Final Advice
In a perfect world, your ammo storage can would have a fresh silicone gasket, a couple of oxygen absorbers and be stacked in a closet inside the HVAC-controlled portion of the house. If that isn’t possible, use the other ideas to lessen the effects of heat and temperature swings.
With guns, I hope they are all kept in the HVAC portion of the house, except for your carry and truck/trunk guns. I will focus on that area, as the rest should not see much effect during summer.
Your carry gun has several things that affect it in the higher-heat environment. The higher the heat, the higher the total humidity. This higher humidity is combined with a much higher likelihood of sweat. Combining the two keeps moist salt in contact with your gun for extended periods. Coupling that with the higher-effective VOC of most gun oils in higher temperatures, makes for less protection in a higher-corrosion environment.
I hope you can see this leading to issues over time. Your truck/trunk gun has very high heat and likely has condensation to deal with in large doses. Rotate the ammo storage and clean the firearm a couple of times between April and October, or you might just find a dusty, rusty, bone-dry gun when you need it.
Conclusion
The takeaway is to clean your carry guns more often and perhaps invest in gun oil with better protection qualities (lower VOC and higher cling). The various all-in-one “CLP” (clean-lube-protect) products are great for light cleaning and light protection. They are not great for removing high carbon build-up or resisting high-corrosion environments. Dedicated cleaning solvents and lubricants are preferred.
What do you do for ammo storage? Were you aware of the heat-related issues? Do you have other ideas? Share your answers in the comment section.
Editor’s note: This post was originally published in June of 2020. It has been revamped and updated for accuracy and clarity.
I have a Liberty Ammo Can Safe. Inside I put a Golden Rod Dehumidifier. In the winter temp average is 50 degrees and summer it is 87 degrees. I was just wondering if this is a good set up for ammo storage. Thanks, Dennis.
My husband has his reloading bench and reloaded ammo
in our garage in phoenix, AZ . no a.c. some of it was reloaded back in the 70s and 80s. Is it safe to shoot? Would it be wrong to give it
To relatives who shoot, after telling them its age and storage history?
As a reloaded for over 40 years I have have learned to take care of many of the issues explained here. Regarding powders along with care in storage, I have always kept all powders in the same environment that I always enjoyed, Air condition a must especially during summer months. I recently finished up a can of Blue Dot that I purchased in 1987 and the results were flawless. I was always reminded as the saying goes, Keep Your Powder Dry!
Good info all around – especially the one about shooting a rifle stored in desert heat – OUCH!
I just found some of my boxed ammo stored in my attic. I had lost track of it, so I know it was subject to 130 degrees for about 3 summers. No one above speculated about what would happen if I shot this ammo today. “Well, it would be degraded.” OK, got it. Here’s a couple other questions: 1) is it possible that I could get a bullet left in the barrel shooting that ammo? That would be expensive – and dangerous. 2) How about taking apart each round and getting rid of the bad powder? 3) If I did take apart all the rounds, how would I get rid of the primer without ruining my de-priming station? 3) Could I soak the brass and primer in water (1 hour?) and then de-prime it in the ordinary way?
Thanks for your help – this represents about 100 rounds. Yuk!
Experienced reloaders also know that heat increases pressure in cartridges. If you’re loading ammo to near-maximum pressures for your firearm, don’t pull it out of your steaming hot car that’s been in the desert sun all day and start firing away. You may have an overpressure situation that could be dangerous.
I am a new gun owner. I’ll start to build a strategy around storing ammo and guns. Thanks for the information
IF you plan to cache or bury your ammunition outside, consider burring it in a bed of SAND. Sand is a good insulator against extreme temperatures differences…
I purchase Silica-gel packets and place them in my steel ammo cans Silica Gel is inexpensive and most importantly WORKS to contain moisture
So, John, what gun oil do you use?
This was a very informative article. I was not aware of all aspects of temperature environment concerning ammo stored in the car garage. I’m a target shooter, once in a while shoot on weekends, I buy ammo from ammo grab stock pile in Harbor freight containers ammo containers, so now I know how the Texas temperatures will affect when stored in the Car garage ..thank you
Question for you-all: I sometimes store ammo in a lacked metal cabinet. This cabinet has things like Paint Thinner or Turpentine on other shelves, which creates that strong smell. If there any reason to believe that this Paint Thinner odor will compromise ammo stored in the same cabinet?
Great article. You covered all the facts. Proper storage IS the key to ammo long life.
I have ammo I bought back in the mid-60’s and it still shoots fine.
I keep my ammo in the house, in ammo cans with two packs of silica and haven’t had any problems.
Thank you for this article several years ago I was doing some research trying to find out how long I can store my ammo this is very informative for me and since I store my ammo inside the house under environmental controls AC and heat keeping my temperature nice comfortable temperature for me the ammo should be just fine it is also stored in military footlocker and sealed am OK hands inside that military footlocker the article does let me know that my carry ammo does need to be rotated though.
To help protect your guns from corrosion, install a golden rod dehumidifier in your gun safe.
What about storage in a gun safe wit a dehumidify?
All my bulk ammo is vacuum sealed. Its all handload, so is also dated. All kept in the house, rotated out probably every 2 to 3 years. I do have loadout kit in the garage safe that probably should be rotated more often, but the number of days my garage gets over 90degs you could count on your hands. Humidity runs about 10% year round in my safes. Relative humidity rarely goes over 28% except during July monsoon flow.
average 80 degrees, average 70% humidity. So Florida no joke. Garage has Central AC and Wall Unit. Lots of Damp Rid when on sale!
I was made aware some time ago, by a friend in law enforcement. I use military ammo cans, stored in my bedroom closet gun safe.