It is a copy of a Marman underhammer. Only parts bougth is Hawkens trigger guard, buttplate and barrelblank.
The plank is straigth octangonal,1"across the flats,33"long, Caliber 54, made by FCI(Charles Burton).
I hand rifled it, twist 1:70 on a bench I barrowed from a friend.
I made the lock...