Return of Zombie Ops is a zombie modification for Call of Duty 4, it features content from Black Ops Zombie mode aswell as from Modern Warfare 3 Survival mode and Ghosts Extinction mode. It's set slightly in the future with some weapons from Ghosts, Black Ops series and Modern Warfare series.
I had this done days ago already but I forgot to upload the screenshots.
Details:
FAD
5.56x45mm NATO Full Auto
Silencer, Muzzle Brake and Grip (though not visible) are options
looks like the original