Lofty,
I have left my gun loaded for a week at a time, I've never had a hang-up or a gun not fire.
The night before I go hunting I clean the rifle really good to remove any oil that might be in it from storage. I will load the gun in the morning and take off hunting. I'm one of those guys that is very careful about not getting my rifle wet or dirty. I still use fff power (haven't made the big change over to 777 or porodex)with number 11 caps I use buffalo bullets for elk and sabits for deer.
I've hunting alot on the westside in the jungle and the rain forests we have and never had a problem so far.