I have no experience with duracoating the metal but I have duracoated the polymer portion of my M&P9 after 1000 rounds still looks good and is showing no real wear.
I think I'd have to agree with ibewiggin and go with Cerakote. I've had it applied to my Star SS and no problems so far. Looks great, too!
I cerakote all guns. Metal slides and polymer frames. I do it all.
Owner/Armorer at Argyle Armoring, LLC - FFL 07
NRA Life MemberWhat do I know? I'm only a professional.