Check out sponsor Armacoat on here for all the diy tips and tricks. For the best finish, the piece should be parkerised first....really good insurance that the paint will adhere, be durable, and protect the metal.
I did an AR barrel with Armacoat 6 or 7 years ago....it was when Murdoc first opened up. I was fortunate that it was already parkd' and to this day it looks as fresh as when I did it. Main thing is to degrease and degrease again, wear dry nylon gloves, make sure you have proper ventilation.... Like not in your house as this stuff is pretty hard on brain cells.