The 455 cylinder was not made for the 45 acp. There is new 455 ammo being made by FIOCCHI
I'm well aware.
But most .455 Webleys in this country have been shaved to take .45ACP, meaning you gotta reload (to .455 specs) if you're not into buying custom loads in (or reloading for) .45 Auto Rim. That Fiocchi .455 won't shoot from a Webley with a shaved cylinder, though it does well enough out of an unmolested example.
It's got small primers, though, which is not as great for some of us who reload.