I'm spraying Norrells OD Green right now.  The temp dropped, so I'll finish tomorrow.

I'm spraying at roughly 27psi.  I'm spraying from 8-10" away, with a medium pattern.  I've used a more narrow spread to coat heavier, but I tend to use it more medium.  I like to finish everything with mist coats from farther back, which also help to flatten out the appearance and reduce sheen.

Make sure you are preheating between coats.

Carb cleaner works fine for me, I washed the receivers in hot soapy water, rinsed, blew them dry, then degreased.  I make sure I am not touching them with bare fingers during this.

There is a "How to" guide hosted in a couple places that walks you through most of the steps.  Its not perfect, but its not bad, and it answers most questions that people have.  If you haven't read it, it may be worth your time.

Norrells AR15 Refinishing Guide