That Gun is a heavily modified, pared down .223 pistol, successor to the pistol from Fallout and Fallout 2. It weighs a hefty 5 pounds and has a motorized cylinder and crane for quicker shooting and reloading than a typical revolver. The green light on the left side turns off and makes a ringing noise once the weapon has reloaded. Until the advent of the Gun Runners' Arsenal it had the unique capability of using dedicated armor piercing rounds, something that no other pistol in the game was capable of.
Along with Lucky, it has the second highest potential critical hit chance (95%) of all one-handed non-energy guns, right after the silenced .22 pistol.
That Gun can fire about 1120 standard rounds, the equivalent of 224 reloads, from full condition before breaking.
It's located in Novac, inside the Dino Bite gift shop. It can either be purchased from Cliff Briscoe, or stolen from the storage room. It is on the end of the first shelf with the Rocket souvenirs to the right. The storage room key can be pick-pocketed or the lock may be picked (very easy). The key may also be purchased during the quest Come Fly With Me or any time after its completion.
If you steal the weapon from Cliff Briscoe and he takes it back from you, it cannot be bought or stolen again.
According to J.E. Sawyer, its name is derived from the fact that many players referred to the .223 pistol as "That Gun from Fallout and Fallout 2."
Like the .223 pistol, That Gun is modeled on the pistol used by Rick Deckard, the main character of the film Blade Runner. This version differs considerably in proportions, and lacks the bolt handle, ejection port, and second trigger.
pcps3xbox360 If you stole That Gun from the storage room, Cliff Briscoe still sells it in his shop, creating the possibility to obtain a second weapon.
pcps3xbox360 If loading a saved game from the main menu in which you have That Gun equipped and drawn, the reload animation takes twice as long as normal. This can be solved by simply switching to another gun and then back again.
pcps3xbox360 That Gun is not affected by The Professional perk. Curiously, its non-unique counterpart, the 5.56mm pistol, is affected by the perk.
xbox360 Rarely, when you are aiming down the sights of That Gun, when you turn right or left the camera will instead pivot from your shoulders, but your gun will stay in the same spot, causing it to careen to the right and left. You can even move your head backwards, to the point that you can see your shoulders in first person.