50 years plus is the usual number for non-corrosive primed ammunition. Corrosive seems to last 75 years plus if stored in decent conditions. The only shotgun shell problem used to be with the now obsolete paper hulls that would swell from moisture.
211 BC: I swear by Jupiter Optimus Maximus .... in the army of the consul Gnaeus Fulvius Centumalus Maximus and for 10 miles around it I will not steal anything worth more than a denarius in any one day.
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