Can I use Fertan Rust Remover Gel to remove rust from a gun?

Yes you can. Fertan Rust Remover Gel will remove the rust and leave the surface ready to be painted or covered in a light oil. Word of caution- on guns that have been blued, it will remove the blued protective surface back to bare metal. It will leave the metal ready to be re-blued via chemical or traditional bluing process.