When I painted my .204 AR with DuraCoat, I called and talked to one of their reps about whether I needed to prime (especially the SS barrel) and was told that it wasn't necessary to do any prep work.... That having been said, I wish I had primed it prior to painting...
Normally, I would use a 'self-etching' primer that is highly durable... It also gives the painter a chance to identify and smooth out any imperfections in the base coating before applying the surface paint..
As a result, I did have a few small spots on the stainless steel that chipped off over the course of the next year and a half and I wound up bead blasting the whole rifle for a repaint...
Now, it's wearing the self-etching primer, waiting for me to decide what I want to do with it...
I will say that, with the exception of the stainless steel portion, the DuraCoat held up pretty well, since I'm not one to 'baby' my tools... I don't believe in abusing them, but they have to hold their own..