Had to look it up, Gas pistol, do you have the 3 barrel type? Rust is not patina, if you have to put a name to rust call it a corrosive metal eater, because that is what it will do if not stopped. With out pictures we can't tell how bad the rust is but what I use for minor rust is a very good light gun oil and 0000 ( 4 0, very fine ) steel wool or even brass wool. Use it very lightly , like rubbing lotion on a baby's butt and then finish with a tooth brush, some use a copper penny ( one ot the older ones, the new penny's are Zinc ) rub out the rust . Others may have different methods or better ideals.