you could try that stove black, heat proof paint for painting wood burner fireplace things & flue (chimney) pipe. The can I have is a matte/satin black with little sparkley things in it (almost a gunmetal black) you spray it on and have to cure it with heat (oven) Might work? Auto shops also sell 1500 degree black spray paint cans (for exhaust pipes/headers)
You ever tried any of that on exhaust pipes or headers. Doesn't last long. Some of the high heat stuff may work on a gun tho. Difference being flame instead of heat.
Duracoat is cheap and easy. This old Smith had most the nickle off of it. I paid $30 for it because it was so ugly. I could see painting a brass frame if you didn't care for the color.