The M4A1 Holo is a modified version of the M4A1 with a Holographic Sight for close quarters engagements and a M203 Grenade Launcher. It can use both standard and suppressed magazines, wich will lower the weapon's range but zombies will react as it was a silent shot. They will still create a normal muzzle flash and sound normal to players.
Along with the M16A2 M203, the M4A1 Holo is one of the few guns with a grenade launcher attached, which can be used by selecting it with the "F" key and having a grenade in your sidearm ammo slots. With this weapon, the flip up leaf sight cannot be used, unlike the M16A2 M203. This makes aiming with the grenade launcher more difficult, making misses a common occurrence. The launcher can fire 40mm grenades of high explosives, flares both white and green and smoke grenades.