I got that as a full length but found it too unwieldy for my T. Rex arms, swapped it out with the shorty folder.
The technique is easy actually, it has to be for me to do it.
I spray all parts with normal B&Q nut brown spray paint, about two coats, nice and even.
Then using cheap as possibly black spray paint (I use poundlands auto spray), spray it onto some kitchen towel from close distance until it just starts to run, then use the towel to make long streaks of black down the stock. This makes e wood grain effect. To blend it in I gave it a good rub with some shoe polishing cloth, then kicked it about in some shingles out back to give it a nice texture and a bit of wear.
Then just use the brown to "mist" over it from a distance to help the paint blend, leave it to dry and it ends up looking like that!
Sorry if it's a bit unclear, I've been down the pub.