The Default Weapon is a secret weapon and base for all weapons, which appears in every Call of Duty game based on Infinity Ward's Quake 3 engine branch. It can only be obtained via console commands on PC or hacking on consoles.
In Call of Duty 2, the left hand is replaced by a strange gray mosaic-like horse and when viewed from third person, it shows a horse with no back end being attached to the player. It resembles odd "finger pistols" with a pink cowbell with text "OWN3D" in Call of Duty: World at War or a small blue box in Call of Duty 4 around the left hand's wrist. The fingers are bent in a strange way.
The weapons have no iron sights, instead zooming the player's view and making the cross-hairs disappear. Using a knife melee attack shows the hands twitch slightly as a knife appears through the back of the left hand. Both hands momentarily disappear from the screen. However, in Black Ops and Black Ops 2, the knife works properly.
The weapon is fully automatic in most games, but semi-automatic in World at War Zombies. The weapon was most likely created for testing purposes and not deleted. It is also possible that it was created for NPCs with no weapon, for example Sgt. Reznov in "Vendetta". In Call of Duty 4, it can kill an enemy with two shots on Veteran difficulty. Despite a popular belief, the Default Weapon does not have unlimited ammo. It has a 10-round magazine, but it does not have an ammo counter. It reloads five shells at a time, which means it must be reloaded twice to fill up the magazine.
The pickup icon is that of a squished AK-47 in Call of Duty 4, Black Ops and Black Ops III.
In Call of Duty: Modern Warfare 3, when looking at a player with the default weapon, it appears to be two gray cones pointing away from the player. The killfeed for it is a squished AK-47.
In Call of Duty: Black Ops II, the killfeed for the Default Weapon is a squished M27. There is a grenade attached to the left arm, however this can only be seen with a FOV changer. In multiplayer if the player tries to switch to another weapon or use scorestreaks while holding the weapon, their console will freeze. This is caused by the Default Weapon not having a proper model to put on the character's back while switching weapons. The default weapon has no in-world model, so if a player dies while holding the gun, everyone in the lobby will get kicked with an error message.
In Call of Duty: Ghosts, the killfeed for the default weapon is a normal looking AK-47. It performs almost identically like it's counterpart in MW3.
The default weapon in Call of Duty: Advanced Warfare is identical to it's Ghosts counterpart. It reuses the AK-47 killfeed icon from Call of Duty: Modern Warfare 3.