In my "stuff" bin I have three rifle actions, all of which need work and then refinishing. These are: Lee-Enfield No. 4 Mk. 1*; M1898 Krag; and non-case hardened Winchester 1886. None has any [additional] value as collectible. I want to eventually metamorphose each one into a useful open-sighted hunting rifle. I have been informed that many semiautomatic pistols being made have dark, nearly black finishes or coatings that are called "black nitriding" or [something to do with] ion finishing. These finishes are claimed to be extremely wear and corrosion resistant. The finish is not on the metal. It is in the metal, having penetrated a surface.
1. If there is such a finish available after market and compatible with my older actions that use simple steel alloys, please identify it.
2. What parts, excluding springs, can be finished without harming a part's heat treat?
3. When parts are finished, do parts reassemble without any "issues?"
4. If you have had a firearm refinished with this process, have used the gun for at least a year, and are satisfied that the finish does what it is purported to do, please identify who did your refinishing job.