The .455 Webley Auto cartridge, also known as the .455 Self-Loading or .455 Webley Automatic, is a British pistol cartridge developed in the early 20th century. It was specifically designed for use in the Webley & Scott self-loading pistols, notably the Webley & Scott Mk I and Mk II models. The cartridge features a rimless design with a bottleneck shape, allowing for smooth feeding in magazine-fed handguns.
The .455 Webley Auto cartridge typically carries a 224-grain full metal jacket (FMJ) bullet, and it was intended for military and law enforcement use, mirroring the performance and terminal ballistics of the .455 Webley revolver cartridge. Its relatively larger projectile was designed for stopping power, making it suitable for military sidearms of the time. However, the usage of this cartridge was relatively short-lived as military forces transitioned to other calibers, and it remains an item of historical and collector interest today.