How long does ammunition last?

Ammunition doesn’t come with an expiration date, but how long it lasts depends on storage conditions, environmental factors and the type of ammo. Properly stored rounds can remain functional for decades or even centuries, while poor storage can cause degradation in just a few years. Whether you’re a shooter, collector, or survivalist, understanding ammo shelf life, signs of deterioration and best storage practices ensures reliability when you need it most. This guide explores how long different types of ammunition last, factors that affect longevity and how to store your ammo properly to maximize its lifespan.

Does ammunition have an expiration date?

Generally, no. That doesn’t mean ammunition lasts forever. When stored properly, modern ammunition can remain functional for decades or even longer. Manufacturers often recommend using ammunition within ten years, but this is quite a conservative estimate. Proper storage conditions are crucial to maintaining ammunition's shelf life. Factors such as exposure to moisture, temperature fluctuations and chemical contamination can degrade ammunition over time.

But how should you actually keep your ammo stored so that it lasts as long as possible?

What affects the shelf life of ammunition?

Moisture and humidity levels

Gunpowder absorbs moisture, reducing burn efficiency and causing misfires. Over time, moisture in the air will impact ammo reliability, corroding primers and oxidizing brass cases, which can lead to malfunctions.

To prevent this, use desiccants (silica gel packs) in storage containers, replacing them every 6-12 months. This isn’t necessary for factory-sealed ammo in climate-controlled environments, but for home storage, it’s highly recommended.

The ideal humidity range is 30-50% relative humidity. Above 60% increases primer and powder failure risk, while below 30% is unnecessary unless you live in a very humid climate. We’d recommend using a hygrometer to monitor humidity levels.

Temperature fluctuations

High heat degrades ammo over time. Exposure above 100°F causes gunpowder instability, affecting performance. Anything over 125°F long-term risks over-pressurization and potential case ruptures.

Heat also weakens primers, leading to ignition failure. Frequent temperature swings (hot to cold) can crack primer sealants, exposing rounds to moisture.

A common mistake is leaving ammo in a hot car, where temps can hit 140°F, damaging powder stability and increasing pressure risks.

For maximum shelf life, keep ammo below 70°F in a stable environment. Avoid storage locations with major temperature swings (attics, garages). An insulated safe or ammo can is best.

Exposure to light and air

Ammunition deteriorates when exposed to direct sunlight, oxygen and moisture over time. UV rays can degrade polymer coatings and cause plastic-cased rounds to weaken, while prolonged exposure to air leads to oxidation, especially in brass cartridges. Over time, this can result in bad ammo that misfires or fails completely. The shelf life of your ammunition depends largely on whether it is stored correctly to protect it from these environmental factors.

Air exposure is particularly damaging when combined with humidity, as it accelerates corrosion on metal components. Most modern ammo is designed to resist these elements, but prolonged exposure over years will still lead to degradation. 

Keeping ammo stored in airtight containers helps prevent this issue. Ammo cans with rubber gaskets create a secure, sealed storage solution that blocks moisture and extends shelf life. For better long-term storage, vacuum-sealing rounds or using VCI (Vapor Corrosion Inhibitor) paper helps reduce oxidation.

Storage conditions

How ammo is stored directly affects how long it lasts. Poor conditions, such as leaving rounds in a garage, basement, or attic, expose them to moisture, temperature swings and dust, all of which can cause damage over time. The best way to store ammo is in a cool, dry place where humidity and temperature are controlled.

Many people make the mistake of storing gun ammunition in places with direct sunlight or high humidity, which shortens the shelf life of ammo. Metal ammo cans offer the best storage solution since they are designed to keep ammo dry and protected from environmental damage. For even better protection, ammo should be stored with desiccants inside sealed containers to absorb excess moisture. 

If you’re storing pistol, rifle, or shotgun ammo, it’s best to keep ammo in its original boxes inside sealed storage containers.

Type and material

Not all ammunition lasts the same amount of time. Full metal jacket (FMJ) rounds, for example, hold up well in storage, while exposed lead bullets can degrade faster, especially in humid conditions. The quality of the casing material also plays a role. Brass-cased rounds last longer than steel or aluminum-cased ammo, which tend to corrode or degrade faster if not stored properly.

Nickel-plated brass is even more resistant to corrosion and is often used in premium pistol and rifle rounds for longer shelf life. Steel-cased ammo, while cheaper, is more prone to rust and degradation when exposed to moisture or air. Aluminum-cased ammo is lightweight but has a shorter lifespan, making it a poor choice for long-term storage.

Shotgun shells require special attention because plastic hulls are more vulnerable to heat, humidity and time. If stored incorrectly, plastic cases can warp, leading to feeding and ejection problems in a shotgun. Storing shotgun ammunition in a dry place is critical to maintaining its performance.

Age of ammunition

Over time, the quality and reliability of your ammo may degrade. Factory-sealed ammo can last decades if stored properly, while old ammunition that has been kept in poor conditions can go bad in just a few years. Military surplus rounds are often decades old but still fire reliably because they were stored correctly in sealed metal cases.

The main risks with old ammo are primer degradation, powder breakdown and case corrosion. Corrosive primers were common in older ammunition, meaning they leave residue that can damage firearms if not cleaned immediately after shooting. While modern ammo is less prone to these issues, it’s still important to check for signs of bad ammo, such as corrosion, case discoloration, or loose bullets. If you find ammunition with rusted cases, cracked shells, or degraded primers, it’s best to dispose of it safely rather than risk using it in a firearm.

For the best results, keep your ammo stored properly in a cool, dry environment with stable temperatures and low humidity. Well-stored ammunition can last a lifetime, while ammo stored improperly can become unreliable in just a few years. Keeping your ammunition in sealed containers, away from moisture and at a consistent temperature ensures that it will perform reliably whenever you need it.

How long do different types of ammo last when stored properly?

Centerfire ammunition

Centerfire ammunition is the most durable, used in rifles, pistols and some shotguns. Its metallic casing and separate primer make it resistant to environmental factors. Properly stored, it can last over 50 years, with military surplus rounds from World War II still functioning today. Brass cases offer the best longevity, while steel-cased ammo is more prone to rust. Excessive heat or moisture can degrade gunpowder and primers, leading to misfires. Storing centerfire rounds in airtight containers with desiccants preserves their performance.

Rimfire ammunition

Rimfire ammo, like .22 LR, is more sensitive to moisture due to its thin casing and primer design. Though it can remain usable for decades under ideal conditions, improper storage leads to primer breakdown and misfires. It should be stored in airtight containers with humidity control to prevent oxidation. Since rimfire rounds are often used for target shooting, rotating stock ensures reliable performance.

Shotgun shells

Shotgun ammunition is less durable due to its plastic hulls, which can become brittle or deform in fluctuating temperatures. Humidity can cause swelling, especially in paper-hulled shells, making them unusable. Brass bases may corrode over time, affecting chambering and ejection. Proper storage in a climate-controlled environment helps prevent degradation and using sealed containers keeps them dry and stable.

Subsonic ammunition

Subsonic ammo is designed for lower velocities and often features modified powder loads or coatings. While its shelf life matches that of standard centerfire rounds, certain coatings can degrade with heat or moisture, affecting accuracy. Because subsonic rounds are often reloaded or manufactured for suppressor use, they may be more prone to inconsistencies. Storing them in sealed containers with moisture control preserves their integrity.

Caseless ammunition

Caseless ammo, which eliminates the traditional metal casing, is more vulnerable to environmental damage. Without a protective shell, its exposed propellant can become brittle or unstable over time. Heat and humidity accelerate breakdown, making caseless rounds less durable than conventional ammunition. Due to these storage challenges, caseless ammo has not been widely adopted for long-term use.

How to tell if your ammo has gone bad

​Determining the reliability of your ammunition is crucial for both safety and firearm performance. Here's how to assess whether your ammo is still good to use:​

Corrosion and tarnish: Examine the cartridge casing for any signs of rust, corrosion, or discoloration. Brass casings may develop a greenish patina, while steel casings can exhibit rust. Such corrosion can weaken the casing and affect the ammunition's performance.​

Physical damage: Look for dents, dings, or deformities on the casing. Even minor imperfections can impede proper chambering or cause malfunctions during firing.​

Primer condition: Check the primer at the base of the cartridge. It should be flush with the casing and free from dents or indentations. A misaligned or damaged primer can lead to misfires.​

Environmental factors: Ammunition stored in humid, hot, or fluctuating conditions is more susceptible to degradation. Moisture can infiltrate the casing, compromising the gunpowder and primer.​

Duration: While modern ammunition can remain functional for decades under optimal conditions, prolonged exposure to adverse environments can shorten its shelf life.​

Test firing: At a controlled shooting range, fire a few rounds from the batch. Monitor for any irregularities, such as delayed ignition, reduced power, or inconsistent accuracy.​

Listen and feel: Be attentive to unusual sounds or sensations when firing. A softer report or reduced recoil may indicate compromised gunpowder.​

Avoid use in critical situations: Refrain from using suspect ammo for self-defense or hunting, where reliability is paramount.​

Proper disposal: If you determine the ammunition is unsafe, consult local guidelines for proper disposal methods. Many shooting ranges or law enforcement agencies offer disposal services.​

Regularly inspecting your ammunition ensures safety and maintains firearm functionality. When in doubt, it's best to err on the side of caution and avoid using questionable ammo.

Frequently asked questions (FAQs)

How long can I store ammo in a magazine?

Ammo can be stored in a magazine indefinitely, but spring tension may weaken over time if left fully loaded. To avoid this, rotate magazines every six months to a year. If stored in a cool, dry place, the ammunition itself will remain stable for decades.

Can old ammunition damage my firearm?

Yes, if the powder or primers degrade, old ammo may result in squib loads (incomplete ignition), which can cause a barrel obstruction. Corroded cases may also stick in the chamber, potentially damaging the extractor or bore. Proper storage minimizes these risks and testing older rounds before heavy use is recommended.

What are the key signs that ammo has gone bad?

Bad ammo shows signs of corrosion, discoloration, or dents in the casing. Loose bullets, cracked shells, or powder leakage indicate instability. Performance issues like misfires, hangfires, or inconsistent power suggest degradation. If any of these are present, the ammo should not be used.

Is it safe to shoot corroded or tarnished ammo?

Tarnished ammo (minor discoloration) is generally safe, but corroded ammo should not be used. Corrosion weakens the casing, increasing the risk of chambering issues, misfires, or pressure failures. If corrosion is visible, especially around the primer or case mouth, the round should be discarded.

Which brands last the longest?

Brands with high-quality sealants, corrosion-resistant cases and strict manufacturing standards tend to last longer. Military surplus ammo often has primers and case necks sealed for extended shelf life, making it another reliable option for long-term storage.