Put some white paint on it then scuff the hell out of it, like on your mag, then wrap some cloth tape around it so you can only see the paint at the top and bottom. If you use a colour of tape lighter than black, coat your hand in something like brown coloured whiteboard marker and hold the grip so the ink transfers. Touch that up and maybe add a little fire ash, to make it look like dirt picked up through hard use in battle.
How's that?
I'll have to post a couple of new ones of my AKS-74U too, because it has undergone a couple of changes.