The most resilient form of gun bluing you can do yourself (easily) is rust bluing. I've done it on many guns. I wouldn't use cold blue on anything except a small repair.
Rust Bluing is easy. I use Mark Lee Express Blue, but Brownells is good also (just takes longer). I hear Belgian blue is very good although I haven't used it. I have also fume blued (An enclosed cabinet with a heat source, moisture source, a small amount of Nitric Acid in one container and a small amount of Muriatic Acid in another container. Parts are left hanging in the cabinet over night. After the parts rust you process from step 5 onward (below).
The rust blue process is very rust resistant when you are done as you have converted most of the freely rustable iron from (Fe2O3) to a black magnetite (Fe3O4). Evidence of this is shown as you are doing this process and the parts rust less and less with each application of solution, as there is less and less available to rust. This is the process that was done on double barrel shotguns as they are largely silver soldered together a very hot or corrosive process could weaken the joints.
1. Strip the old bluing off. You can use bluing remover (50/50 water and muriatic acid and the bluing just disappears, then neutralize well). To brighten up the metal use 400 grit wet or dry paper (wet) and buff the metal.
2. Clean the metal well, from here off it's latex gloved to prevent finger prints.
3. Warm the metal parts over a clean flame (gas not a wood fire) till they are almost too warm to handle.
4. Rub the rust blue solution on in long even strokes.
5. Boil for about 15 minutes in Distilled Water (yes is should be distilled, depending on your mineral composition of your tap water you can get streaks or uneven coloring).
6. The red/tan rust the was on the gun converts into a black, kind of velvety coating. you buff this off with a carding wheel or carding brush. Carding is just a fancy word for brushing off the parts with a very fine brush made of .002-.003 dia bristles (they're very soft). This will remove the fuzziness but not the color.
Depending in the iron content you may have to do this up to 10 or more
times, but to be honest I rarely have to go over 5 or 6.
Here is a French SACM M1935A that I did.
Bluing Solution Applied
After multiple applications, final carding and oiling
Any questions let me know.