Do it yourself jobs turn to Brownells Aluma-hyde. Best there is in a can. They have a few good colors: Olive Drab, Coyote tan, Flat Black, ectt. Even have a black grit spray for forearm and palm areas. Prep work is the key and they even have stuff for that too. They have very knowledgeable customer service.
Keys: Completely strip gun apart
Proper prep work by removing ALL oil and grease--Contact Brownell's
Tape up everywhere you dont want the paint.
Warm conditions to paint (Above 72 degrees minimum, but i think 80 is way better) and adequate time to cure properly(depending on environmental temp. , but 30 days is good)
Their stuff is as tuff as you can get for do it yourself applications and impervious to most all strong cleaning products and solvents