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Unless you've been soaking it with oil, good ammo will fire many decades after manufacture. (And even if oil-soaked, it's still likely to work just fine.)

I understand the cost issue, but when it comes down to it, your life may depend on it working, so AT LEAST on a yearly basis, you ought to fire your carry ammo in practice and replenish it with fresh stuff. (A fresh box of ammo per year isn't much.)