Interesting to me was the one he had loaded for 3yrs and all 6 went BANG without a hitch! Ive kept em loaded for 6mos to test it one time and had the same result.... That being said, I still wouldnt make it standard practice.
It's well documented that Hickock would fire empty his revolvers, clean them, and reload them at the beginning of the day, then go about his day's business. But that was a personal thing with him.
The other end of the range, I have some personal experience with. A fellow had a cap & ball revolver in a display case. Family heirloom, had been in that case for at LEAST 80 years. And, apparently it was loaded! He never bothered to check, might not have even known, UNTIL, while he was away one of his son's took the pistol from its case to show some friends, and FIRED a shot!!!
No one was hurt, thankfully. The guy brought the gun to our local smith to be "unloaded". The smith took it, went back to his test fire barrel, and fired off the remaining 5 shots without malfunction . After the smoke cleared, literally, the smith gave the guy a quick lesson on cleaning, and loading the gun.
As mentioned, black powder, stored right, will last almost indefinitely.
For defensive use, the standard .36 cal cap&ball has about the energy of a .380ACP. However, the soft lead round ball makes it more effective than a .380ACP FMJ.