Hardwoods Camouflage Howto
Masking
Mask off any vital areas with 3M Painters Tape. This may include things like open bolts, hopper feed tubes, etc...
Basecoat
Apply the basecoat.
This should be done slowly, and evenly.
It is better to apply 5 light coats than 1 heavy dripping coat.
Initiate the spray before you reach your marker, that way you have a nice fine mist hitting your gun. If you start right above your marker you risk globs and splotches. Not good. Not good at all young jedi.
Experiment with distances. If you spray from too far back, the paint particles will glob together making a nasty orange peel looking finish. For my airbrush 3 inches seemed good.
Let the basecoat dry. 1 hour air dry. If you are using Duracoat, I recommend waiting a full day for it set up as it will allow the paint to degass. The degassing can make the adhesive on the stencil material more sticky, hindering their removal later on.
Stenciling
Start placing stencils with the assistance of your xacto blade. Do not press them down until you are happy with the position. Once you are happy, press them down to make sure they stick.
TIP: if you find that the stencils are not sticking to curved or raised edges, use a hair dryer to warm the vinyl. Then press the stencil down again, it should stick now.
Here i laid down a basecoat of Woodland brown. You could easily use black, or even both.
I then added the branches fairly randomly, trying to tie the branches together at the tops and bottom of the rifle.
Next I applied a nice white coat. I then felt it needed a bit more pattern to break it up. So i grabbed my Iwata airbrush and applied some nice smoke-like lines to it.
And here is a mask i did using the same technique.

And Finally a Remington done by a customer.