Breechloading muzzle-loaders ARE intriguing. I have a GILBEY'S Patent -- British patent #620, 12 March 1853
Made by H Esau ACKRILL, Beverley, Yorkshire. 60bore capping Breech-Loading rifle, #12. It has a spring-loaded hinged chamber operated by button latch in the LHS. Tubular cap magazine to butt (access to cap magazine through trap in steel butt-plate), automatic raising of magazine "aperture" for capping when the hammer is half-cocked. When the breech lock button is struck the chamber flies back and (in theory!) the nipple enters the aperture and is capped.
As a safety feature in case of a breech explosion there is a steel lined vent tube from chamber mouth at front of action through the fore-end, venting forwards. To keep the left hand out of the way the trigger-guard is flat faced (like some Adams / Tranter revolving rifles). I understand that Ackrill made at least one double-barrelled version (not seen).
APOLOGIES for the photos-- not had time to edit them -- - too busy organising the "Repeating Pistol Meeting" at Bisley.