Does Ammo Expire? Storage, Shelf Life, and Real-World Conditions

How Long Does Ammo Actually Last?

Modern centerfire ammunition manufactured with non-corrosive primers (everything made since the 1950s by major manufacturers) has an essentially indefinite shelf life when stored properly. There is no chemical expiration clock. The propellant doesn't decompose under normal conditions. The primer compound remains viable for decades. The brass case doesn't corrode in dry environments.

Military collectors regularly fire WWII-era .30-06, Korean War-era 7.62 NATO, and Vietnam-era 5.56 without issues. The key variable isn't age — it's storage conditions.

Rimfire (.22 LR) is more sensitive than centerfire. The priming compound is distributed around the rim of the case and is more susceptible to moisture penetration. Old .22 LR stored in poor conditions has noticeably higher dud rates than old centerfire. But even .22 LR stored in sealed containers lasts for many years without problems.

The Three Enemies of Ammunition

1. Moisture

Water is the primary threat. Moisture corrodes brass cases, degrades primer compounds, and can seep past the case mouth or primer pocket to contaminate powder. Corroded ammo may still fire, but reliability drops. Green or white oxidation on brass is a warning sign — inspect the primer pocket and case mouth before loading it.

2. Extreme Heat

Propellant chemistry is stable at normal temperatures but can degrade at sustained high heat. SAAMI testing shows ammunition is safe at temperatures up to 150°F for short periods. Sustained storage above 120–130°F accelerates powder degradation over years. A hot attic in Arizona or Texas (which can reach 140–160°F in summer) is a bad long-term storage location.

3. Temperature Cycling

Repeated expansion and contraction from daily temperature swings can loosen the bullet-to-case seal and the primer pocket seal over time. A garage that goes from 40°F at night to 110°F during the day is worse than a consistently warm (but not extreme) closet.

Real-World Storage Scenarios

How to Store Ammo Properly

The Gold Standard: Military Surplus Ammo Cans

.50 cal ammo cans (M2A1/M2A2) are the best consumer storage option. They're steel, airtight (rubber gasket in the lid), stackable, and built to survive decades of military use. You can find them at surplus stores, gun shows, and online for $8–$15 each. Each .50 cal can holds roughly 1,000 rounds of 9mm or 500 rounds of 5.56 in their original boxes.

Desiccant Packs

Drop one or two silica gel desiccant packs (40–60 gram) into each ammo can before sealing. These absorb residual moisture inside the container. Replace or recharge them annually — silica gel can be recharged by baking at 250°F for 2 hours.

Alternative Containers

MTM Case-Gard plastic ammo cans and Plano ammo boxes work well for organization but aren't truly airtight like surplus metal cans. If using plastic containers, store them inside a climate-controlled space. Original manufacturer cardboard boxes are fine for short-to-medium-term storage in a closet but offer zero moisture protection.

Carry Ammo Rotation Schedule

When you rotate carry ammo, shoot the old rounds at the range. This serves double duty: you confirm your carry ammo fires reliably, and you get practice with your actual defensive load instead of just range FMJ.

Signs Your Ammo May Be Compromised

Green or white corrosion on the case: Inspect the primer and case mouth. Light tarnishing is cosmetic and harmless. Heavy corrosion with pitting suggests moisture damage — segregate and dispose of these rounds.

Bullet pushed deep into the case (setback): Compare suspect rounds to fresh ones from the same box. If the bullet is visibly shorter, the round is overpressure — do not fire it.

Dented or cracked cases: Don't fire them. The case may fail to contain pressure, causing a case rupture.

Loose bullets that wiggle: The case mouth seal has failed. These rounds may still fire but accuracy and pressure will be unpredictable.

The Bottom Line