I turned this up after some looking about....it just go`s to show that even if one has never heard of the cartridge, it dosent mean it dosent exist.

7338 .425 Webley 1 5/16", round nose I groove lead, copper primer with waffle pattern, headstamp
P.W & S + .426 +, made by National Arms & Ammunition Co for P. Webley & Son for use in
the Webley Kangaroo rifles, from display with 2 holes in one side of case, varnished $90.00

Also found this in response to a search which suggested the roo rifle pill was in here,didnt find it under 425 though there is some good stuff here,worth a look. It came up under 425 kanga

http://rtbltd.com/arch/cats/1203_06.pdf