Loading protocol: powder, lubed felt wad, ball. No grease.
Use a ball of the proper size and caps that fit and chain fires will not be a problem.
Propellant: real black powder, Pyrodex, Triple 7 - all are stable, with real black having legendary long term stability.
Now the lecture:
There is no, repeat, absolutely no good reason to store a bp revolver loaded for any more than a month, and preferably a week. If you're going to use the gun for self defense you absolutely MUST be fully proficient with it. You're betting your life on that gun and your ability to use it - why would you accept anything less than full, top of the line performance from either the gun or yourself? And how in the world can you be proficient if you haven't fired the gun even once in several months? The simple fact is you can't.
Take the time to find an accurate, reliable load and shoot it once a week at least Get proficient, to where you can place your shots where you want them every time, and stay that way with frequent practice. If you don't, then you're just playing cowboy and you're not serious about using the gun for self defense.