I noticed most who paint their ARs use low priced rattle can to do it. Some will try Cerakoting, which is the hardest of the firearms coatings to apply, IIRC.

Why don't more people try something like Duracoat, KG Guncoat, or one of Brownells spray-on finishes for firearms? It provides a nicer finish than rattle can and is easier to apply than Cerakote, IIRC. I think there is a rattle can option to apply Duracoat.

Note: I have no affiliation with any of the above companies or products.