> Loads for the 455 Eley are very similar to the 45 Schofield and 45 Autorim
Those are a bit hot for the Webley. It was popular to skim the back of the cylinder so that 45acp in moon clips would fit it, but 45acp is hot for the gun.
I guess that Hornady brass would be the Mk II brass, which is shorter then Mk I. I think Mk II brass is 3/4 of an inch long, where Mk I was 7/8th so I don't have any reloading data.
I would just mention that the gun needs a soft lead hollow base bullet to shoot well. The exit diameter of the cylinder chambers is .450" to .451" and the barrel is .455"ish. The hollow base allows the bullet to expand to grip the rifling. 45acp bullets (.451 to .452) don't get much of a grip after being sized down by the cylinder throats. While that all sounds weird, the gun was expected to fire 450 Adams, 476 Eley or 455 Webley, depending on what was in stock in your part of the Empire at the time.
There are 2 popular moulds out there. RCBS and NEI. I prefer the NEI as the lube groves on the RCBS are hard to cast well unless using a lot of tin in the lead alloy.
Have a good time with it !