I know of a Hawken .54 caliber that was purchased at an estate sale last year. The gun was last afield in 1971. After inspection, it was determined to have been put away with a charge and ball in the barrel. The charge fired!!

And, incidently, the bore condition wasn't real bad. The area where the charge had been against the walls of the barrel for 35 years was pitted; but the rifling ahead of the ball was fairly decent. I guess this is a testiment to the dry conditions out here in the western states.