I don't like using steel wool on guns.
My old method is to soak the rusty area with a good penetrating fluid like Kroil or CLP Breakfree for 1 or 2 days. This softens and loosens the rust.
Then apply more fluid and liberally scrub the rusty area with a brass "toothbrush".
This won't harm the bluing.
Once the rust is off, wipe clean and keep a thin coat of CLP Breakfree on the gun to prevent further rust and to continue "working" on any remaining rust.