The Colt Eley .455 mark II case is longer than the Mark I case and extends beyond the cylinder stops in a Webley revolver. This therefore is a far better option (the Mark II case) for the Webley because the metal in the base of those cylinder stops is paper thin. The Hornady cases are Mark I's.Lee put out good reloading dies for the .455 Webley and their powder specs should be adhered to and not exceeded. The correct military bullet is thrown from the .455- 265 grain round nose hollow based bullet R.C.B.S. mould.
I would stand by those who caution the use of factory .45 a.c.p. ball ammunition. The Webley isn't strong enough an action.