If it is steel, does it looks like it might be painted black, or does it looks more like the "blued steel" on a gun barrel? The rust can probably be removed with very fine ("0000") steel wool, but even this can scratch off the blackening. Is it also dirty, or was it carefully...
A gel containing phosphoric acid is what is callednaval jelly,a thick gel that can be applied to surfaces to remove rust. Phosphoric acid is also a component of soft drinks leading to lowered bone density. It is also used in dentistry and orthodontics as an etching solution to clean and ro...
You really don't want to slop ammonia (especially if heavily concentrated) all over the blued parts of the gun (as it will likely start to remove bluing after 30 minutes or so) and you also shouldn't leave the ammonia in the bore for an extended period of time (like hours, although ...
Polish the parts to be blued. Again, steel wool or 600 to 1200-grit sandpaper will work to remove any loose rust, scarring, or pitting from the gun metal. If you plan to remove the gun's finish from the factory before bluing, some recommend using a phosphoric acid-based automotive ru...