Well the percussion hammer whacks a percussion cap which is filled with a chemical mix similar to the priming compound in a cartridge primer. It ignites when struck and the flame goes down the hole in the nipple into the load of black powder (and ONLY black powder.)
A flintlock swings an actual piece of flint rock against a piece of steel ( the frizzen) and strikes sparks which fall into a priming pan of very fine black powder on the side of the barrel and ignites it. The flame goes through a flash hole into the barrel and lights the full load of black powder.
I guess you could call Mr Blissett a one off maker. There were few standard models in those days, except for military weapons, the makers turned out guns to order or made what they thought would sell.