What I've used in the past, but not on rifles or pistols, is roll cage paint. Takes a long time to cure.. but it's pretty solid afterwards.

I've had pretty good success with krylon, but the kicker is i've done enough at this point where i have screwed up a few things and had to start back at scratch. My biggest thing is I hit what ever I paint with about 3 to 5 thin layers of matte clear. I have a tar I painted at the beginning of last season and its still pretty damn good looking with just minor wear on the cheek rest and handle.

Not sure but if you guys are interested in plastidip I have a supplier locally here in Toronto who can get it.
All kinds of colors.