Hi, Hand Rifle Guy,
A lot of Webleys, especially the Mk VI, were converted to use the .45ACP with half moon clips, and they will also use the .45 Auto Rim. BUT, they are not strong enough for any long term use with .45ACP factory ammo or equivalent, as the .45ACP has a higher velocity and pressure than the original .455 ammo. The gun will suffer battering at the lock and will gradually stretch. If using one, it is best to load the .45ACP or .45AR down to .455 pressures and use lead bullets.
Jim