[Slamfire]

I asked a Naval Insensitive Munitions expert about the lifetime of primers, and he said “indefinite”. Since then I have conducted my own studies on primers and have come to the conclusion that the lifetime of primers is much longer than the lifetime of gunpowder. So from an insensitive munitions viewpoint, “indefinite” is a reasonable answer. A rule of thumb for a safe storage lifetime for gunpowder is 20 years for double based, and 45 years for single based. Lead styphnate primers have a lifetime exceeding this as long as they are not exposed to humidity and heat. Heat evidentially degrades primers. I don’t remember what temperatures dud out primers, but assume it is bad to expose primers to a constant exposure to temperatures above 150 F. Primer mix is made wet and the water baked out. Once dry it is very dangerous. A sealant is put above the primer cake to keep it dry and sealants are very good. I have never tried this, but I don’t see a reason why wet primers won’t dry out.

Chlorate primers, the old corrosive primers, had a finite shelf life, but it had to be as long as lead styphnate.