I have used 3 types of paint to coat rifles/barreled actions.
1 rustolium camo flat spray paints, works ok, I used it over some of the "stone texture" paint for a 3d look. effective, semi durable, but not professional. Hoppes will take the stuff off if you let it soak more than a few minutes.
2 Dry flim coating done by airborne coatings. this company coats mostly exhaust systems for cars, but our local branch here in OKC has an entire line that is low temp enough (they are baked on) that you don't have to worry about the metalurgy of the steel, and in colors ranging from flat black, to bright pink. There are a few IPSC and IDPA pistols around here sporting their Sky blue, Chevrolet orange, and hot pink finishs. Great for metal parts, but you can't do stocks. I have had 4 guns done in this finish, one of which I gave as a gift, if that gives you some idea what I think of them. Extremly durable, and cheap. Really cheap. Cleaners won't touch the stuff.
3 duracoat done by my gunsmith. Also very durable, though not as scratch resistant as the dry film. This stuff is great for doing camo on whole rifles, and looks very professional when they are done. MUCH more expensive than the dry film coating. Safe for solvents too.
Personally, the next camo rifle I build will have a stock/ rings/scope done in durocoat camoflage, with the barrel reciever/bottom metal done by airborne in OD green.