Alan, I have spoken to Vere Bressler and he tells me your rifle is an Alex Henry calibre. Very rare. He has a cartridge for it and will send me dimensions etc. The cartridge is in the Eley Catalogue of 1901. He has come across an Alex Henry falling block which he has just purchased and has seen a double rifle in that calibre. Have you looked in Hoyam's four volumes on cartridges? I believe you will find it there. Vere is going to dig out his Hoyams for us on that and if he finds it will fax me a copy of the relevant page