Joshua's Pistol Whippin' .45

Joshua's Pistol Whippin' .45 is a non-playable weapon

Gameplay
As a companion, Joshua Graham will use this weapon when prompted to use Melee Weapons. As the name implies, it is Graham's unique .45 Auto pistol, A Light Shining in Darkness, held by the barrel and used to "pistol-whip" enemies with the butt end of the gun.

Its special V.A.T.S. attack is called "lights out." It is considered an improved holdout weapon, meaning it can be taken into weapon-free places like casinos, provided the player's Sneak skill is 50.

Location
Joshua's Pistol Whippin' .45 cannot be used by the Courier without the use of mods or console commands.