Tips for removing heavy rust from a gun?

if it is HEAVY PITTING, I would suggest takeing it to a gunsmith. Remember that Blueing is a form of Rust, you dont want to further damage the cosmetics of the gun by removeing blueing with the rust. Some OTC chemicles WILL DO THIS, so be careful if you try this at home. Other than that, if its just Light surface rust, I agree with Pyro, some 0000 steel wool lightly worked over the area with some GOOD gun oil will do the trick. just remember to remove the excess oil. Good LUCK!