The krylon comes in heat resistant gloss or matte(flat) finish. Duracoat has always been flat in my experience. I'm having trouble finding the heat resistant krylon in matte black but I'm definitely sure its out there. They also have a rust resistant version.
Some links to help you out
YouTube - Broadcast Yourself.
^ how to spray paint ar-15. They use a lower receiver but the idea is the same with a barrel. Just make sure you cover both holes and don't let any paint get inside.
"To prohibit a citizen from wearing or carrying a war arm . . . is an unwarranted restriction upon the constitutional right to keep and bear arms. If cowardly and dishonorable men sometimes shoot unarmed men with army pistols or guns, the evil must be prevented by the penitentiary and gallows, and not by a general deprivation of constitutional privilege." [Wilson v. State, 33 Ark. 557, at 560, 34 Am. Rep. 52, at 54 (1878)]