I have had a few Webley 455 cylinders in for throat honing, and I am going to tell you, those things are HARD! The steel they use in them is quite tough and time consuming to hone so that makes me wonder how strong the revolver is and what kind of loads will they handle?
Throats on those guns typically run .449" .450" while the groove diameter is an honest .455" they seem to work much better with throats in the .455" ~ .456" range, I have gotten good range reports from the ones I have honed.