Hi
Take a look at my model 28.When my Dad joined the Police Dept. in 1960 he bought this and sent it to Texas for Armaloy coating.At the time the big selling points were resistance to corrosion and holster wear.This was carried daily for over 30 years so you can judge whether that was true or not.
Armaloy is still in business and does quite a bit of govt. contracting for various things.
Yours really looks like an Armaloy coating.
Bob