The first hunt I used my mk85 on it rained for 5 days. When I got home I had quite a bit of rust on barrel where the stock covered it. From that point on I have used Birchwood-casy sheath on all the metal of my gun. I do not run it down the barrel but everywhere else. Since that first hunt I have zero rust on nmy gun. Sheath is now called Barricade. Its works so well that I have no fear at all that weather will negatively affect my gun again. The inside of my barrel gets a light oil patch after a cleaning. Before I go hunting I will fire one cap against a patch, and then run one clean patch down. My barrel on the inside almosts looks new.