Just saw a custom halfstock rifle, nicely made, that is unlike any I have seen before. Instead of having a drum and nipple, or a patent breech, the nipple is screwed directly into the slanted flat of the octagon barrel, just about where the breechplug ends. The otherwise normal percussion lock has the hammer bent over to the left, so that the hammer impacts the nipple in the barrel. Very neatly done and probably works well. Why it was done this way I can't guess. No pictures but you can search a certain well-known gun auction site and search on "D Bowman" to see good views of this rifle.