PS,
Cordite wasn't corrosive, it was errosive. The high flame temperatures actually burned, rather than rusted, the steel out of the barrels.
Mercuric primers aren't a problem, it is the corrosive component, potassium chlorate, in them that ARE the problem. The mercury attacks the case brass, but not the barrel steel.
The potassium chlorate attacks the steel through its residue attracting water, causing rusting, but it doesn't affect the brass.
The old primers would get you coming AND going!
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Beware the man with the S&W .357 Mag.
Chances are he knows how to use it.