Black Bart's Bane

 is a unique B.B. Gun.

Location
This weapon can not be found anywhere in the game. It is obtainable only via console command on PC.

Behind the scenes
Its name is a reference to A Christmas Story. Ralphie, having just received his new Red Ryder BB Gun, takes aim at a target across the yard and mumbles "Okay, Black Bart... now you get yours!"