Pretty much any paint will work. Ive used Testors model paints for years, and it works great and they come in pretty much any color you need if you want a camo job.
I stripped the paint off a shotgun that had been painted for over 25 years and used pretty heavily in that time, and the finish underneath looked like the day it was painted. No hint of rust, and no wear, where the paint covered things. If you allow the paint to wear off at the wear points, you do lose the protection. Easily touched up though.
Ive used Aluma Hyde II on a couple of guns. It works well, but you need to follow the instructions to the letter. Also, if you change your mind later, youre going to need a bead blast to get it off. Things like Testors and Krylon (not sure about Krylon Fusion on plastics though), will come off fairly easy with solvents.
When applied right, Aluma Hyde II looks more like a finish than a paint. Ive done a couple of early SAR1 AK imports, that were pretty rough finish wise with it, and they came out looking great.
The other thing you can use it for is a base. Ive done that with a couple of cammo jobs. AHII as the base, and Testors on top. The Testors came off later, and the AHII stayed and showed no real damage from the removal.
If you paint with any of them, prep is the key. Degrease everything well, including your hands, and have things set up beforehand (how you plan on hanging, handling the gun, etc), and youll have a better experience doing it.
Brownells has a couple of videos on painting things and using their paints. Lots of good info there, even if you arent using their paints.
If you want the gun to look like it came from the factory, Id use the Aluma Hyde, or one of those type paints. If you want to cammie the gun for hunting, Id go with something like Testors or Krylon, etc,.
This is a Testors/Krylon job.....
New.....
Over the pattern its trying to mimic...
About 10 years of pretty constant use....