How long does ammo last?

How long does ammunition last?

There is no single expiration date. Federal publishes a figure: "If stored properly, loaded ammunition and reloading components have a 10-year shelf life" (Federal FAQ). SAAMI, the industry standards body, describes it in terms of conditions rather than years: ammunition kept in factory packaging "subject to the ordinary variations of temperature and humidity ranging from tropic to Arctic conditions, can be expected to perform satisfactorily and safely" in the firearm it was made for, while extreme heat above 150° F should be avoided (SAAMI, Small Arms Ammunition: Properties & Recommendations for Storage & Handling).

Read together, the published guidance is that ammunition does not have a fixed life that runs out on a date; it degrades in response to heat, moisture, and chemical exposure. The 10-year figure is the manufacturer's stated shelf life for properly stored product. It is not a statement that ammunition fails at year eleven, and it is not a guarantee that ammunition stored badly will last ten years.

What damages ammunition in storage?

SAAMI's storage pamphlet lists the exposures that cause problems and what they do:

• Heat and humidity. "Extended exposure to high temperatures and/or high humidity may damage ammunition. This damage may result in increased or decreased chamber pressure, incomplete burning of the propellant, or failure to fire" (SAAMI, Recommendations for Safe Ammunition Storage and Handling).
• Water and chemicals. "Exposure to water, solvents, petroleum products, acids, ammonia, and other chemicals can damage ammunition," including through corrosive effects that weaken the case or make the cartridge hard to chamber. If moisture or chemicals get inside the cartridge, the result may be failure to fire, incomplete burning, or delayed firing (same source).
• Vehicles. SAAMI advises against leaving ammunition "inside a vehicle (including the trunk) for extended periods in direct sunlight or at elevated temperatures," because doing so "can accelerate the deterioration of the propellant" (same source). The older SAAMI leaflet notes that the passenger compartment of a closed car in the sun "often develops an extreme high temperature."
• Repeated handling. Rechambering the same cartridge over and over "may cause physical damage to the case," can damage the primer pellet, and can push the bullet deeper into the case, which raises chamber pressure (same source). This is a handling issue rather than a storage one, and it applies most to rounds that are loaded and unloaded repeatedly, such as carry ammunition.

Primers, the most sensitive component, respond to the same conditions. SAAMI's primer guidance says primers "should be kept dry and not exposed to high temperatures (more than 150° F). If exposed to wet conditions or high temperatures, they may deteriorate, yielding misfires or poor ignition of the propellant powder" (SAAMI, Sporting Ammunition Primers).

How do storage conditions compare?

The table restates the published guidance by condition. It describes what the sources say about each factor; it does not rate storage locations.

What container do manufacturers specify?

SAAMI's guidance is that "ammunition should be stored in its original packaging or other packaging designed for the purpose," noting that manufacturers package ammunition to meet U.S. Department of Transportation and international transport standards (SAAMI storage pamphlet). Speer's FAQ says the same in shorter form: "We recommend storing ammunition in cool and dry conditions in original packaging," and refers to SAAMI for the full recommendation (Speer FAQ). The older SAAMI leaflet adds a practical reason for keeping the factory carton: its labeling helps make sure the ammunition is later used in the firearm it was made for.

Ammo cans and desiccant. Metal and polymer ammunition cans with a gasketed lid are a common way to keep cartons dry, and silica-gel desiccant packs are often added to absorb moisture inside a closed container. Neither SAAMI nor the manufacturer FAQs cited here specify a container brand, a gasket type, or desiccant use; what they specify is the outcome — cool, dry, away from chemicals and heat. A sealed container addresses the humidity part of that. It does not address temperature: a sealed can in a hot attic or vehicle is still exposed to the heat that SAAMI identifies as damaging.

Does rimfire ammo last as long as centerfire?

The two are built differently. SAAMI defines a rimfire cartridge as "a rimmed cartridge design in which the rim is formed with a cavity to contain the priming mix," while a centerfire cartridge "has its primer central to the axis in the head of the case" (SAAMI glossary). In a centerfire round the priming compound sits in a separate primer cup seated in a pocket; in a rimfire round it is spun into the fold of the case rim itself.

That construction is why SAAMI treats them differently around moisture. Its guidance on water exposure says centerfire rifle, handgun and shotshell ammunition is "reasonably tolerant of exposure to light rain or dropping in the snow or on damp ground as long as the exposure is limited, and the cartridges are wiped dry immediately," but that "rimfire ammunition is much more susceptible than other ammunition types to moisture damage from exposure to the elements, due to the unique construction of the cartridges" (SAAMI, Guidance on Ammunition That Has Been Submerged in Water).

None of the manufacturer sources cited here publishes a separate shelf-life figure in years for rimfire. What the published guidance supports is narrower: rimfire is more sensitive to moisture, so the "dry" half of cool-and-dry matters more for it. For more on the most common rimfire cartridge, see the .22 LR caliber page and .22 LR plinking and target loads compared.

What about ammunition that got wet?

SAAMI separates two cases. Light, brief exposure — rain, snow, damp ground — is tolerated by centerfire ammunition if it is wiped dry immediately. Ammunition that has been submerged for any length of time is different: because depth, duration, primer sealing and contaminants all vary, SAAMI states that "the safe answer is to NOT attempt to salvage or otherwise use previously submerged ammunition" (SAAMI submersion guidance).

The hazards it lists include degraded propellant from attempts to dry cartridges with heat, primer failure, and a partial ignition that leaves the bullet lodged in the barrel — a bore obstruction that can cause a catastrophic failure if another round is fired behind it. SAAMI directs owners to dispose of submerged ammunition according to local, state and federal rules, to contact local law enforcement for disposal guidance, and not to ship it back to the manufacturer.

How do you check old ammunition?

SAAMI's handling guidelines call for inspecting ammunition before use and disposing of "cartridges or shotshells that show signs of physical damage, such as corrosion, deep dents and/or scratches," with the instruction: "If in doubt, do not chamber or fire the ammunition" (SAAMI storage pamphlet). The same document says ammunition should chamber easily, and that a cartridge requiring abnormal force to close the bolt or breech should never be fired.

Corrosion of that kind shows as discoloration or deposits on the case, or rust on a steel case. Corrosion on the outside of a case is a storage symptom; it is unrelated to whether a primer is corrosive, which is a property of the priming compound and is covered in corrosive vs non-corrosive ammo.

How does storage relate to buying in bulk?

Case quantities — 500 or 1,000 rounds — usually carry a lower cost per round than small boxes on a listing basis, which is why storage questions often come up alongside bulk buying. The storage guidance above is the same at any quantity; what changes is how long a given quantity sits before it is used. Tracked case prices are on bulk 9mm and bulk 5.56, and the arithmetic of comparing listings is in how to buy ammo online.

Case material matters too: steel cases are lacquered or polymer-coated to resist rust, and brass is a copper-zinc alloy. The trade-offs between them are in steel case vs brass case.

Related articles

• Corrosive vs non-corrosive ammo
• Steel case vs brass case
• How to buy ammo online
• Ammo shipping restrictions by state

Sources

• SAAMI — Recommendations for Safe Ammunition Storage and Handling
• SAAMI — Small Arms Ammunition: Properties & Recommendations for Storage & Handling
• SAAMI — Sporting Ammunition Primers: Properties, Handling & Storage
• SAAMI — Guidance on Ammunition That Has Been Submerged in Water (rev. 2/26/2025)
• SAAMI glossary — rimfire and centerfire definitions
• Federal Ammunition — FAQ — shelf life and storage
• Speer — FAQ — storage recommendation