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 experience in the Comment section.
Editor’s note: This post was originally published in June of 2020. It has been completely revamped and updated for accuracy and clarity.
