Assuming that when the gun did go off, it went off properly, meaning that the powder itself was not bad, the gun was dirty. There was fouling, crud, or who knows what in there somewhere. Fouling actually sucks moisture out of the air. If you leave your gun dirty while hunting you are asking for trouble. I have not seen a problem arise in just a few hours though.

I hunt with a clean, dry barrel/breech/nipple. No fowling, oils, lubes - nothing.