Store all your firearms in a cool, dry place, with a dehumidifier running nearby for good measure if there is any hint of moisture (as in a basement). But if you pull out one of your guns and see a few blotches of rust on barrel or receiver, here’s an interesting way to remove it.
From Range 365: The trick…is finding a penny minted before 1982, which were 95 percent copper and 5 percent zinc.
To start you need some light oil (good old 3-in-1 will do just fine), a medium brass-bristle cleaning brush, some paper towels, and your pre-1982 penny.
Pick a spot to start, put some oil on the metal, rub the penny over the area, and wipe clean with a paper towel. Repeat until the rust is gone. Use the brush to scour the rust out of areas with small crevices, like a shotgun rib.
The copper in the penny is softer than the steel, so light pressure will wear away the rust without scouring the steel or the remaining bluing.