Matt - unfortunately it is a shotgun converted some time ago but it was at a dealers who did not want a lot for it as it had been cut down. It shoots round ball ok at 25 metres. Single barrelled cartridge bore rifles are, I believe quite rare
There is an excellent example of a single tip down 10bore Alexander Henry rifle with octagonal barrel in Wal Winfer's book - I would love that!

Mike - Is your serial number anywhere near mine 68XX? (PM me if you do not want to detail here)
It is quite late for the hammer rifles, maybe earlier locks used up? Possibly the Duke got a deal for the 3?

Huvius - as you say, less usual but there seems to be little consistency with front, rear or non bolted locks.

Many thanks for your positive comments

TH44