Quick Answer: Store ammunition between 55°F and 85°F at 50% relative humidity or less, per SAAMI’s own guidelines — humidity corrodes brass and primers faster than heat degrades powder in a normal home environment. Despite the “10-year shelf life” many boxes print, ammunition kept cool, dry, and sealed with a desiccant routinely remains fully functional for 50 to 100 years or more; sealed military surplus ammo from the 1940s-1960s still fires reliably today as living proof. The printed shelf-life figure is a conservative liability estimate, not a technical expiration date.
Ammo storage advice online ranges from “it lasts forever” to “replace it every few years,” and neither extreme is quite right. The real answer comes down to two environmental variables — temperature and humidity — and one habit most owners skip: an airtight container with a working desiccant.
SAAMI’s storage guidelines at a glance
| Factor | SAAMI-recommended range | What happens outside it |
|---|---|---|
| Temperature | 55°F - 85°F | Powder degradation accelerates mainly above ~150°F; big daily swings (garages, car trunks) are worse than steady heat |
| Humidity | 50% relative humidity or less | Moisture corrodes brass cases and primers, causing misfires and split cases over years |
| Container | Sealed, airtight (ammo can or safe) | Open shelving exposes rounds to ambient humidity swings and dust |
| Desiccant | Recharged every 6-12 months | A saturated desiccant stops absorbing and can no longer protect against humidity spikes |
The “10-year shelf life” myth
Ammunition boxes and manufacturer FAQs often cite a roughly 10-year shelf life, and it’s easy to read that as an expiration date. SAAMI itself doesn’t publish a specific shelf life at all — its position is that degradation comes from environmental exposure (heat cycling, high humidity, repeated temperature swings), not time passing on its own. The 10-year figure that shows up on some packaging is a conservative number manufacturers can stand behind for liability purposes, not a physical limit.
The practical evidence backs that up: ammunition stored correctly — cool, dry, sealed, with a maintained desiccant — routinely remains fully functional for 50 to 100 years or more. Military surplus ammunition manufactured in the 1940s through 1960s and stored in sealed cans with desiccant still fires reliably today, which is about as strong a real-world proof point as this topic gets. The failure mode isn’t a calendar date, it’s a container that let humidity or repeated heat cycling in.
Eva-Dry E-333 Renewable Mini Dehumidifier
- Crystallized silica gel with a color-change indicator window (orange = needs recharging), per Eva-Dry's own spec sheet.
- Fits inside a gun safe, ammo can, or storage cabinet without drilling a power-cord hole.
- The single cheapest upgrade against the actual cause of ammo degradation: humidity, not time.
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Choosing a container
Sealed steel ammo cans like the Solid Tactical 50 Cal or a genuine military-surplus M2A1 use a rubber gasket to keep moisture and pests out entirely, and they’re cheap enough to buy several and organize by caliber — but they offer no meaningful theft resistance and no fire rating on their own. Gun safes add real security and, if UL- or ETL-rated, real fire protection, but a tight door seal traps ambient humidity just as effectively as it blocks heat and smoke, so a safe full of ammo still needs its own desiccant. Original factory boxes inside either container add a layer of organization and keep headstamp and lot information visible, which matters if a round ever needs tracing back to a bad batch.
MTM Case-Gard Ammo Boxes
- An O-ring gasket on the lid keeps moisture out even if the outer can or safe seal is imperfect.
- Sized per caliber, so rifle and pistol rounds don't end up mixed loose in one bin.
- A fraction of the weight of steel, useful for owners who move ammo between a safe and a range bag often.
Where not to store ammo
Avoid attics, uninsulated garages, sheds, and vehicle trunks — not because a single hot day ruins ammunition, but because those locations combine the two worst conditions at once: large daily temperature swings and uncontrolled humidity. A steady 80°F closet is a better environment than a garage that swings from 40°F at night to 110°F in direct summer sun, even though the garage’s average might look similar on paper. Basements are usually fine for temperature but can run humid, which makes a desiccant non-negotiable rather than optional.
The bottom line
Keep ammunition sealed, between 55°F and 85°F, under 50% humidity, with a desiccant you actually recharge on schedule — that’s the entire SAAMI-backed guideline, and it’s enough to get 50+ years out of a box most people assume is good for 10. For organization, MTM Case-Gard boxes sorted by caliber inside a sealed steel can beat loose rounds on a shelf every time; see our best ammo can roundup for specific picks. If that storage lives inside a gun safe, our gun safe humidity control guide covers keeping the whole interior — firearms and ammunition both — rust-free, and our gun safe fire rating guide explains what a fire-rated safe actually buys the ammunition stored inside it.