I did a complete re-blue with cold blue on a Ruger GP-100, just because I didn't want to spend any money on it, when I'm done using it, maybe I'll have it professionally done, the blue job came out very good and has been durable. Even though it is cold blued, it seems to hold oil quite well.
IMO the key to any type of bluing is metal preperation, if you skimp on prep it will show no matter what type of blue process you use.
When rust bluing a barrel I seal the muzzle and throat so I don't get anything in the bore, the last one I did I used foam earplugs with a light coat of non hardening sealant on them, sort of glued them in, just a regular bore cleaning removed any trace of it.
NRA Lifetime Member Since 1999
"I ask, sir, what is the militia? It is the whole people except for a few public officials." George Mason