Cadet - If you do not have it, Wal Winfer's Vol. 1 of his "British Single Shot Rifles" Alexander Henry, is essential, but now may be very difficult to source. (There is one in the US on Abebooks NOW)
There are also updates is some of the later volumes

Jonathon Kirton's "The British Falling Block Breechloading Rifle" has a section on him
(also on Abebooks now)

They are not cheap but IMHO essential for serious study

TH44

Note on re reading this thread, Double rifles are not included - sorry