Airgun Guru: Stop your rifle going rusty

Q: A friend found small surface rust spots appearing on his airgun over the course of last winter. Apart from regularly wiping gun oil onto the steel, are there any other precautions we can take to stop rust from forming? I don’t want my own rifles going rusty!

GURU SAYS: The clue to the most probable cause of rust forming on your friend’s rifle is that it happened during the winter, and the culprit is temperature. Presuming that your friend was shooting outdoors in very cold conditions last winter, the temperature of his rifle would fall as it acclimatised. The cold is not in itself a problem, as long as the rifle remains in cold and dry air, but sooner or later, the rifle will be moved into a warmer air environment, which could be inside a car during the journey home, or the air in the owner’s house, and that’s when the trouble starts.

The colder air is, the denser it is, which means that it cannot hold as much moisture as when warm. As temperature rises, the air becomes less dense, and is capable of holding more moisture. So when you turn the car heater on and the air warms, moisture from your breath is able to be absorbed into the air and the humidity rises, and the same is true of the conditions inside a house.

When warm, moist air touches the cold steel of the rifle it is rapidly chilled, which makes it denser and squeezes out the moisture, which condenses onto the surface of the steel, and that’s the cause of the rust on your friend’s rifle. It’s not just external surfaces that suffer condensation, either, because water will condense just as readily onto internal steel surfaces.

The solution to preventing condensation and consequent rust is very simple; when you finish any shooting session in cold temperatures, wipe any moisture from exposed surfaces, then place the rifle in a gun slip and make sure the zip is fastened fully to seal in the cold, dry, air and keep moist warm air out. Keep the rifle in its slip for two or three hours after taking it into a warmer and higher humidity environment, whether it’s your car or house, which will give it plenty of time to warm up. When the rifle has acclimatised, it can safely be removed from the slip with absolutely no chance of moisture condensing onto it and causing rusting.