How rare it is, I could not really say... I also never saw one in a percussion. In fact when I saw it for sale, I expected a flintlock. When I saw the picture of it, I questioned the owner about it. It is a Pennsylvania Hunter model if that makes a difference.. The others are I believe called Pennsylvania Rifles. So maybe the Hunter part opened the styles up.. Just like T/C makes a Renegade and then they make a Renegade Hunter. The hunter model only has a single trigger.