I have successfully used perma blue and would recommend it
however I use it differently, I clean and polish the metal to be blued and pour boiling hot water over it before applying the perma blue solution
I then leave it overnight, when I see it the next morning it is rusty really rusty, I then spray the rust with wd40 or similar and steel wool the rust off
then do it all over again, till you have the required finish, when you want to stop spray the job and leave it a few hours to stop the chemical reaction
polish it off and keep oil on it, obviously a gunsmith can do a better job
here's one I did a while ago with perma blue
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