The round block '02 Webley wont take a 30-40 without troughing out the top of the block. The rim is too big in diameter and in stock form, the block doesn't drop far enough to allow it.
It may fit if you don't mind holding the lever down all the way when you load it and then pushing the case home against the extractor while closing the action...
I think the 30-40 would be far too powerful for this action anyway.