The .357 Revolver was a 6-round, semi-automatic revolver manufactured by Spearhead Armoury and chambered in .357 LR. It was entirely ineffective against Xenomorphs. However, it was fairly effective against humans and Working Joe Synthetics.
In 2137, the revolver was standard issue for security aboard Sevastopol Station. It was also used by many residents aboard the station, especially when a Xenomorph Drone was birthed aboard the station. Notably, Axel and Amanda Ripley, who found hers on a table aboard the station, used revolvers aboard Sevastopol.
The revolver is one of the first weapons acquired in Alien: Isolation, found in Mission 3 - Encounters on a white table in the Lorenz Systech Spire. As is typical for revolvers, it can hold 6 rounds in its cylinder. Ammunition for the revolver can be found in cabinets, containers, etc. or looted from corpses. However, revolvers themselves cannot be taken from corpses, even if the player doesn't currently have one in their inventory.
As with all projectile weapons in the game, the revolver doesn't have any meaningful effect on the Alien. It can, however, be used to shoot propane tanks next to the Alien, which will force the creature into the vents if it is close enough to the explosion. Unlike the Alien, other human survivors and standard Working Joes can be killed with the revolver, usually taking 2 to 3 and 5 to 6 hits, respectively, although hitting a foe's head will reduce the amount of shots required to kill.
One of the major drawbacks of the revolver is that firing it creates a lot of noise, which will alert other survivors and Working Joes, as well as attract the Alien (if the player is in an area it can appear in). This can, however, be used to the player's advantage if they want to lure an enemy into a trap or summon the Alien to dispatch humans. Another drawback is the reloading process; as Ripley loads one round at a time, it can be a time consuming process.
In Mission 13 - Consultation, the player is forced to leave her revolver and other weapons at a security check to access APOLLO. However, another revolver is found and picked up as the player descends toward Sevastopol's reactor core.
Behind the scenes
The .357 Revolver appears to be based on the Chiappa Rhino, an Italian revolver that fires from the "6 o'clock" barrel position (bottom chamber of the cylinder) and can fire .357 rounds, like the .357 Revolver (although the Chiappa Rhino fires Magnum cartridges, while the .357 Revolver fires LR).
While the .357 LR centerfire cartridge that the revolver fires is fictional, it is presumably based on the aforementioned .357 Magnum cartridge, as well as the .22 Long Rifle, ".357" indicating that it has a .357-inch (9.07 mm) bullet diameter and "LR" presumably standing for Long Rifle (as is the case with .22 Long Rifle, which is commonly called .22 LR).
A possible in-universe explanation for why all weapons found aboard Sevastopol, including the revolver, cannot kill the Alien is because they are purposely designed to have weak penetration capabilities in order to avoid a hull breach, which would be a catastrophic event on a space station. However, the Alien's invulnerability to the .357 rounds fired by the revolver seemingly contradicts the 1986 film Aliens, where Private Vasquez kills an Alien with a few 9×19mm Parabellum rounds (which are similar in size to the revolver's rounds) fired from her Smith & Wesson Model 39 at point-blank range into the Alien's head; though difficult to attempt without modding the game to make the Alien less aggressive, shooting the head of the Alien in Alien: Isolation from a similar distance will not even create a mark in the creature's exoskeleton.
- The revolver is one of only two traditional firearms in Alien: Isolation, the other being the Model 37-12 Gauge Pump Action, a shotgun.
- On October 29, 2014, a mod by user "Tau34RUS" was added to the Fallout: New Vegas of the site Nexus Mods allowing the revolver from Alien: Isolation (with some slight differences) to be used in the video game Fallout: New Vegas. The same user later added a mod on November 8 that allows the flamethrower to be used in the game.