Stainless is an "alloy" that comes in many grades. If it's pure stainless, a magnet won't stick or pull on it at all... Try a magnet on your gun...
I've spend weeks at a time, on the Alaska peninsula, where at times the weather will be unbeliviable. I've seen all kinds of rust, but not all blued guns rust the same. My drilling spent long hours in the rain/snow/freezing and thawing all on the same trip, and it just didn't rust! Why? beacuse the blued steel is "properly" rust blued, and a good rust blueing "really" resist rust. I never did more than wipe the bbls off to get the water droplets off it, same with a good color case. After more than 20 years, i sent my drilling in to have the triggers lightened, and to be given a through cleaning. The smith said it had NO rust inside, and just needed a minor cleaning...
I remember one brown bear hunt, where 3 guys came along. They were a sorry mess, their tent blown down, they were cold and one was shakeing bad from exposure! I let them stay in my camp, where one of them had a model 12 Winchester. He was sitting there crying, looking at how rusty "granpa's" shotgun was... I took a small piece of aluminum foil, crumpled it up, dipped it in bacon grease, and started in on the rust. He was shocked at how much rust that foil would take off, and he did the whole gun, saving it from needing a re blue.
Taking the metal out of the stock, putting paste wax on the metal, and putting it all back together does keep the rust as bay... This is a fairly common trick in Alaska, that we did waaaay back in the 70's... I've left guns for weeks like that, and cleaned them after the trip.
While halibut fishing, nothing keeps guns from rusting... Even some stainless guns will rust when a drop of salt water hits them and sits there a while... I use to carry a S&W M-18 22lr revolver a lot on salt water fishing trips. I had it "Nitexed" to keep the rust at bay, it worked pretty good, but it's NOT a great looking finish... Does anyone else have a gun that's Nitexed?
DM