Lots of stencils are used. It takes a lot of patience and a sharp exacto knife to cut them out. Getting the right material is also a tedious.
It isn't a simple first timers task. At least that's what I think. I've been messing with the airbrush, nozzles, and paints for awhile now but can't seem to settle on a pattern.
So far, I've figured that the stock would be painted with the largest area covering color (base). No stencil. Then a stencil covering the next largest area of color and so on until you get it the way you wish.
Google on duracoat for some good patterns.
Planning ahead is a real plus. Practice on the wife's fridge is also recommended before tackling something really valuable like your rifle.