Masterkey

The Masterkey shotgun is an available underbarrel attachment for most assault rifles in Call of Duty: Black Ops.

Campaign
The Masterkey is a rare attachment found in the singleplayer campaign. It can be found on the level "S.O.G.," mounted to the player's starting M16. In the same level, the Marines will occasionally drop an M14 with this attachment when killed. It is also found on the 2nd part of "Rebirth," on Hudson's Enfield, along with an Infrared scope. If the player searches around in the submarine base on Redemption, they may find a Galil with the attachment.

Multiplayer
The Masterkey shotgun can be purchased for. It is compatible with most assault rifles, with the exception of the G11. It is comparable to the Stakeout, as both shotguns have the same magazine capacity, but the Masterkey has a slightly higher rate of fire, less range, and the Masterkey deals 30-10 damage while the Stakeout deals 40-10. The Masterkey has a smaller spread than the Stakeout. The Masterkey also does not suffer from a larger spread while moving, with an exception being the Masterkey on a Commando.

In comparison to the Flamethrower (attachment), the Masterkey is capable of a one-shot kill to an enemy of full health, while the Flamethrower will kill in 2 "shots" of the projected flame. However, should the shot miss, or not kill, the pumping cycle could prove fatal in a firefight, whereas the continuous stream of fire emitted from the Flamethrower will not suffer from this risk. Another advantage that the Masterkey boasts is the ability to kill enemies with Flak Jacket Pro.

Using Steady Aim will increase the 1-shot kill range of the Masterkey. Although it has a moderately slow reload, it's more worth having an ability to add more punch to the Masterkey. Steady Aim Pro will further increase the Masterkey's ability as a close quarters as the fast recovery makes it a good 'panic' weapon. This is especially true on weapons that suffer when the player is forced to fire from the hip at close range such as the FN FAL, M14 and M16.

It also frees up the player's secondary slot for the player to have a Launcher or Special, and in most cases it is as quick, if not quicker, than switching to a pistol. The Masterkey should not be used with Warlord because it is a waste of a perk, as when using the Masterkey, a second attachment cannot be used.

Zombies
It is available on the Pack-a-Punch version of the AUG, and seems to do relatively high damage, even comparing to the Stakeout. It sports increased damage and will reload two shells at a time. However, it starts to lose its ability to kill in one hit at about round 17.

Trivia

 * When wielding a Masterkey, the player will grasp the pump with the left hand, but the trigger is not touched.
 * Out of all the underbarrel attachments, the AI opponents in Combat Training will only use the Masterkey, but can equip the Grenade Launcher or Flamethrower.
 * The shots come out of the barrel of the gun it is equipped to instead of the attachment itself.
 * Before entering the rat tunnels in Victor Charlie, it is possible to find an AK47 with a Masterkey with an 8 round magazine.