Not an AR, but still a gun part. Still letting the paint dry off, but it looks good. I've posted it here before how I get my Multicam, but here it is again:
I used Desert Sand for the cream splotches. For the dark brown splotches, I used Black misted with Earth Brown. Next layer, I used Earth Yellow (misted with Light Green), and Dark Green. Final layer I used Earth Brown, Khaki, and Light Tan. Negative stenciling to generate the patterns (traced from a Multicam rifle case), all paints were from Aervoe's Camo or Digital Camo line.