On my conceal revolver probably once every 3-5 years. That doesn't mean I just load them and let them sit. I shoot/clean the gun every few weeks and inspect every round. Also helps that I load with nickel plated brass. After about 5 years I shoot the rounds off, replace them, and have never had an issue.

With my semi-auto I change out the ammo every year.

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Ephesians 6 (Armor of God)