Artic/Keith - thank you for your replies, that's helpful.
I've not yet fired the gun, but it deserves to be being an Alexander Henry (1879). The bores and chambers are in excellent condition. Ran a bore scope through and really don't think it has been fired very much at all since being re-barrelled in 1888.
Do plan on doing a Cerrosafe chamber cast, as you suggest, not least to have a better idea of the precise dimensions. They do chamber a 450 inert cartridge cleanly.
I remain looking for a source of available dies and will look to see if Huntington's can ship UK.
