Field Note · July 20, 2026
How Long Does Ammo Last? Storage and Shelf Life
Ammo doesn't have a use-by date stamped on the box, and there's a reason. Stored right, factory ammunition holds up for a long time — years to decades, not months. Stored wrong, it can go bad a lot faster. Here's what actually matters for keeping your stockpile good to fire.
No hard expiration date
Modern factory ammo is built to last. The brass case, primer, and powder charge are stable components, and under decent conditions they don't break down on any fixed schedule. There's no calendar date where a box of ammo flips from good to bad.
One caveat worth knowing: most standard ammo is not truly sealed against moisture. Some loads — military-spec or anything marked waterproof — have sealant at the primer and case mouth, but ordinary range and hunting ammo usually doesn't. That's exactly why storage does the deciding: the clock that matters isn't time, it's how the ammo was treated. A box kept cool and dry for a long stretch can easily outlast a box left in bad conditions for a much shorter one.
What actually ages ammo
Three things do the damage: heat, humidity, and big temperature swings.
Heat speeds up the slow chemical breakdown of gunpowder over time. Humidity is worse — moisture works into primers and powder, and it corrodes brass cases from the outside in. Swinging between hot and cold, especially with humidity along for the ride, causes condensation to form inside containers and on the ammo itself, even when it looks dry to the eye.
A garage, attic, car trunk, or shed that bakes in summer and freezes in winter is rough on ammo even when it's never technically wet.
How to store it right
The goal is simple: keep ammo cool, dry, dark, and sealed.
- Store in a cool, stable-temperature space — a closet or basement beats a garage or attic
- Keep it out of direct sunlight and away from heat sources
- Use sealed containers; military-style ammo cans with a good gasket are the standard for a reason
- Add a desiccant pack inside the container to soak up ambient moisture
- Avoid repeatedly opening and closing containers in humid conditions — that's how moisture gets trapped inside
- Rotate stock so older ammo gets used first instead of sitting untouched for years
When to walk away from a box
Rimfire — .22 LR especially — is more sensitive to moisture and age than centerfire. The priming compound sits right at the rim, more exposed, so poorly stored rimfire tends to show problems sooner. Store it with the same care as centerfire, or more.
Whatever the caliber, look ammo over before you load it. If you see any of the following, don't chamber it — set it aside instead:
- Heavy corrosion or green/white buildup on the case
- Corroded, pitted, or discolored primers
- Cracks anywhere in the case
- A bullet that's loose or shifted in the case mouth
- Ammo that's been submerged in water or stored somewhere it clearly got wet