The .45 Auto pistol is a single-action, semi-automatic, magazine-fed handgun that utilizes .45 Autoammunition. While the .45 AP improved sights modification was cut from the game, the sights are still present on the weapon's default model (pre- and post-modified versions). This gives the .45 Auto pistol luminescent sights, and as such, it is very effective in caves and dark areas.
Furthermore, it is considered an improved holdout weapon and can be taken into weapon-free locations with a Sneakskill of 50 or greater. It also has the highest base damage of any silenced holdout weapon once the AP silencer mod has been added.
The .45 Auto pistol can fire a total of about 745 standard rounds, the equivalent of 107 reloads, from full condition before breaking. When modded with the heavy duty slide, it can fire a total of about 1,120 standard rounds, the equivalent of 160 reloads, from full condition before breaking.
.45 Auto pistol improved sights – it appears as though there may have been an "upgraded iron-sight" mod available for this weapon but it was cut from the final release, and the weapon's default model uses them instead.
It can be purchased from the Gun Runners, Great Khans, Chet from Goodsprings, etc. after returning to the Mojave Wasteland. (The Gun Runners will have a 98% condition gun every three in-game days, also Gun Runners will restock attachments for .45 Auto pistol every three in-game days.)
It can be purchased from Joshua Graham. Two or three of them will reappear in his inventory after he arrives at the Sorrows' camp.
Although Graham is seen inspecting countless amounts of these pistols when talking with the Courier for the first time, only four in poor condition can be stolen from Joshua Graham's desk in Angel cave.
Some of these are used by tribals in Zion.
There is one in good condition in a footlocker behind Joshua Graham in Angel Cave.
The .45 Auto pistol is based on the Colt M1911, although it is not an exact replica.
It is also one of two guns in Fallout: New Vegas based on real-world weapons designed by John Browning, the other being the automatic rifle. Browning was also a member of the Mormon church and served as a missionary in Georgia. 
Playstation 3Xbox 360 If both mods are attached and you use a weapon repair kit on it, the weapon stops degrading from use and can continue to be repaired past 100% increasing its value and condition. [verified]
PCXbox 360 Sometimes, when both modifications are attached to the .45 Auto pistol, it will not show in first person or third person view while in the Mojave Wasteland. [verified]
PCPlaystation 3Xbox 360 If loading a saved game from the main menu in which you have the .45 Auto pistol equipped and drawn, the reload animation takes twice as long as normal. This can be solved by switching to another weapon, then back again. [verified]
PCPlaystation 3Xbox 360 Sometimes when aiming down the sight while in first person view, the gun will disappear entirely. Switching to another weapon, then back seems to fix the issue. [verified]
PCPlaystation 3 Sometimes, when ED-E repairs the weapon with both modifications, the condition will actually degrade instead of improving. [verified]