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

Yes you can. Fertan Rust Converter will convert the rust into an inert dust. Once this inert dust is removed via wet sponge or a light stream of water you will have a black Zinc Phosphate coating left on the metal. Word of caution- on guns that have been blued, it will remove the blued protective surface and leave a black Zinc Phosphate coating. At this point you can paint the gun, or remove the zinc Phosphate coating by sanding or gentle scrubbing to get the gun back to bare metal if you wish to re-blue it by chemical or traditional bluing process. The Black Zinc Phosphate coating will protect your gun up to six months before needing to be primed/painted or removed so that you can re-blue your gun.