I have kept a cap and ball revolver loaded for two years, and it fired fine. Seemed like it had full power.
I put 28 grains of black powder in the .44, and the ball, no wad.
I put no wax or grease on the ball or cap. Just setting in a drawer, it doesn't look like much humid air would get past the cap, or the ball.
I have been thinking of trying the beeswax on the cap and over the ball, it certainly couldn't hurt.
I have a .44 in the drawer right here that has been loaded for 3 years.
I might take it out tomorrow and try it out.
I will put up some boards and try a penetration test, compared with a fresh reload.