Leaving your BP loaded for a prolonged period of time will cause pitting in your barrel in the area of your powder charge. It does not matter if it is SS or not. Even a small amount of humidity will do it. This is first hand knowledge for I use to do it as well. Furthermore even a small amount of moister will cause a variation in the charge which could cause not necessarily a miss fire but a missed shot at longer ranges. This has happened to me. Fortunately my fresh follow up shot was on its mark. I still leave my round in good weather for a week or so but never longer. It cost me $200 to fix my gun from these practices and I hope to save you the same unnecessary expense. You can by one of those compressed air gizmos that will safely unload your gun without firing it. If you are like me and like your firearms in perfect condition please learn from my mistakes.
I agree, short periods only in dry weather. Wet weather you need to load each hunt.