If you can keep the rifle where there will be no temperature changes it should be ok, however, if the temp changes from warm to cold or vise versa there is a good chance the barrel will sweat, making your powder wet and making a problem to unload and reload. I just saw this happen with a guy who had left a load in his percussion rifle, we were on a hunt and the day before he went out to make sure it was still on target and all he got was caps going off. He removed the nipple and he had mush in the barrel. Better to shoot it, clean it and reload the day you hunt than to take a chance.