About ten years ago, as an experiment, I left my '60 Army loaded for almost six of them. Five cyl's fired just fine, the other one I didn't load. No rust or corrosion.
Whatever you do, don't leave a rifle loaded with a wet patch or wet patch and pyrodex especially. Good friend of mine did that back in the early '80s, I learned a solid lesson from his mistake. I load with the powder charge, then a dry wool or fiber wad and patched ball lubed with a grease type lube, whatever I happen to feel like using at the time, SPG, mutton tallow, mink oil, LOOB, etc. I like SPG the best and usually have some on hand for black powder loads in cartridge rifles.