|Name||The Equalizer or the Hammurabi|
|Manufacturer||God aka Chuck|
|Powers||Can kill anything.|
|Location/Owners||Destroyed by Lilith|
|Episodes|| 14.20 Moriah|
15.01 Back and to the Future
So, this doesn't so much fire bullets as it sends a wave of multidimensional energy across a perfectly balanced quantum link between whoever's shooting it and whoever they are shooting at.
This weapon was created by Chuck to kill the Nephilim Jack Kline. Chuck's suggested names for the weapon were the Equalizer or the Hammurabi, both of which elicited only confused looks from the Winchesters and Castiel.
After Chuck decides to end the world, Dean leaves the Equalizer in the Impala's glove compartment in case they need it. However Lilith, whom Chuck revived and sent to retrieve the gun, manages to destroy it.
The gun does not fire bullets, instead employing a wave of multidimensional energy using a balanced quantum link between the target and the shooter, causing whatever happens to the target to also happen to the shooter. According to Chuck, the gun is capable of killing anything.
Castiel proves to be unable to heal the wound it inflicted upon Sam, stating that the wound has an energy he has never felt before. The shot also has a negative effect on God, who in His wounded state is no longer at full strength or complete, and is afraid. The bullet creates a quantum link between Sam and God, causing Sam to feel pain from the wound when God does. Sam is also capable of seeing into Chuck's mind, witnessing the various possible endings to his stories where one brother kills the other in the form of nightmares.
Chuck presents the gun to the Winchesters and Castiel as the only weapon capable of killing Jack Kline. However, He warns that whatever happens to the target also happens to the shooter, meaning that whoever kills Jack will die as well. Chuck explains that this is why He can't kill Jack -- because if He dies, the universe ends.
In a cemetery, Dean confronts Jack with it, but can't bring himself to kill Jack, instead dropping the gun. This enrages Chuck, who demands Dean pick up the gun and kill Jack, going so far as to try and entice Dean by promising to bring Mary back. But when Dean still refuses, He begins smiting Jack. As Chuck is about to leave, Sam grabs the weapon and shoots Chuck, hitting Him in the shoulder and injuring himself at the same time. However, it fails to cause Chuck any real harm, only angering Chuck enough that He decides to end the world, unleashing the souls of Hell upon the Earth.
Sam continues to carry the wound he got from shooting Chuck. After healing Sam's knife wound from John Wayne Gacy, Castiel attempts to heal the gun shot, but receives strange visions of Sam and tells him that he cannot heal it as the wound is emitting an energy he has never felt before. Dean later treats the wound and notices that the bullet has no corresponding exit wound.
Chuck is revealed to be suffering negative effects from Sam shooting Him with the Equalizer. Amara senses that Chuck is now no longer complete, not at full strength, and afraid. Chuck and Sam are shown to share a link, with Sam feeling the pain Chuck does when He touches the wound. Amara later states that Chuck has been severely weakened and while He can still do "a few parlor tricks," He is trapped on Earth and can't leave or heal His wound without her help. Amara refuses to help Chuck, likening His state to when He once trapped her.
Sam continues to have more nightmares -- one where he is possessed by Lucifer and Dean tries to kill him before Sam immolates him instead, and another where Dean is affected by the Mark of Cain and kills him with the First Blade. Chuck revived Lilith to have her retrieve the Equalizer, and after Lilith reveals that Chuck's favorite "ending" to the Winchester story is where one brother kills the other, Sam realizes that the Equalizer "shot" a piece of Sam into Chuck, and that he is seeing into Chuck's mind and experiencing God's different endings.
Lilith threatens to kill Sam, making Dean reluctantly take her to their motel room. This turns out to be a ruse so Sam can shoot her with a devil's trap bullet, allowing the Winchesters to make their escape. However, Lilith manages to remove the bullet and immobilize the brothers. She deduces that the gun is in the Impala's glove compartment and uses her powers to melt the gun in her hands before taking her leave.