As an experiment, I once let a loaded and capped BP revolver go 4 full years with real black powder. The Crisco in the chamber mouths had dried up and shrunk a bit, so I smeared some new stuff on, stepped outside and all six went bang, no problem. No corrosion and no problems firing.
Three years ago I put a couple of loaded cylinders away and left them alone until a month or so ago. The load was 35gr pyrodex p, vegetable fiber wad, lube cookie made from beeswax and lard, 220gr conicals that I cast myself, cci #11 magnum primers that fit perfectly on the nipples. The cylinders stayed in the top of the closet of my storage room in which I've closed the central heat/air vents so it gets a little warm in summer, a little cool in winter. One pretty day I decided to see if they fired and if so how well...was curious to see if they developed the "pop...boom" syndrome or if they were dead. Well I was happy to get BOOM X 12!
No hangfire and no decrease in power from a fresh load (as far as I could tell). That was a good day shootin, I put 24 more shots through each cylinder...just for the heck of it.
It's near impossilbe to get real black around here so I've almost always used pyro p...but I don't mind gettin dirty and smokin up the neighborhood, to me it's part of the fun!