Birchwood-Casey 2 In 1 and Kano AerKroil are all I use for my two break-action MLs. They remove everything.... carbon, copper, lead, plastic residue.......etc. My centerfires see a third product, for they both are semi-auto gas guns. For the moving action, I use Ballistol for the slides, action and exterior of all my guns.
I take Ballistol to deer camp and use it exclusively there, for everything maintained during hunting week there. The best part of taking it, is nobody wants to come near it and borrow it, for it stinks bad and the homeowner every year threatens to ban me from his home for bringing it.
There are so many rust-inhibiting (not rust preventative) gun oils on the market to protect it long-term after that. They are a dime-a-dozen. The best rust-buster is a nice, dry environment that surrounds your stored MLs.