This is a Lee Enfield rifle, its a world war one rifle, and it fits on marines/riflemen without any guns or any custom that uses the rifleman or marines' attack animations.
Edit, fixed screen shot, Fixed wrapping on metal top
Edit, i fixed the wraping on the stock on anarchainbedlam's specs
Btw, the back part looks a bit worse then the front but you cant see it ingame
Keywords:
Lee Enfield, World war one, World war, World War 1, The Great War, Infantry, Gun, Rifle, Gunpowder, Chuck norris RULZ, trench