Try using Turtle Wax Chrome Polish and Rust Remover.
It has an extremely fine polishing compound in the liquid it will remove fine rust without removing the underlying blue. 0000 steel wool will remove bluing so be really careful with it.
The model 58 in my avatar was the sidearm a motorcycle officer carried for years. It was so freckled and covered with fine rust I thought the finish was a lost cause but the Turtle wax Polish and rust remover removed all the rust and left what bluing remained . I worked slow and took my time but when completed and then waxed the old girl looked good , considering the hard life she had led.
Gary