This is yet another custom skin for Zombie Panic! Source.
I found the default Winchester to look too rusty, old, and plain. So with this new looks it might make you say "This, is my BOOMSTICK!" Because in game I found I picked up the Winchester more then the other shotguns. This a definite must get for more enjoyable experience with the Winchester.
In order to get this skin to work follow this tutorial on how to make custom zps skins work for you.