IRL as far as I know most Webleys were/are chambered for a proprietary .455 caliber round but could theoretically load .45 ACP. I wouldn't recommend trying to shoot .45 out of one though because it's a higher pressure cartridge than .455 Webley which is honestly kinda sad since .45 ACP is already a "fat and slow" if highly reliable round. I'll be amazed if it gets armor penetration but it's definitely going knock the person wearing the armor down into the dirt.