Whats the reason for the paint? Is it to try to restore the original as close as possible, or are you doing it for another reason?
I've been painting guns since the 60's. Most of the time, it was camo jobs, and mostly using Testors Military Flats with a couple of three clear flat lacquer over coats. I still have guns that have been painted with the same paint about 20+ years now. I've also stripped guns of those paint jobs and never found a speck of rust under them, even after that long. These were "high use" guns too.
If your going to use one of the more gun specific type paints, be aware, your probably going to have to bead blast them to get them off in the future, unless you just paint over them.
Testors, will come completely off with some work, and it looks like Kylon will too, but I've only had limited experience with it now to say for sure. It seems to come off like the Testors though.
Brownells makes a couple of good gun specific paints. When applied according to their directions, you will usually get very good results. They also have some good videos you can watch on their web site addressing application, which also works well for other paints too. I've used their Aluma Hyde II a lot, and with real good results. Done everything from guns and accessories to bicycles.
I reparked my MP5, and then repainted over that with Aluma Hyde II in matte black. This is what the results were....
Same gun with the factory finish on the A3 stock.....