Jim Whisker's book, "Arms Makers of Pennsylvania" shows a nice William Schreckengost over/under rifle. It has a "mule ear" lock with two separate hammers. Nice looking gun.
There was a whole family of Schreckengost gunsmiths who settled around Putneyville (Armstrong County) PA.
The Jefferson County (nearby) Historical Society has hosted a gun and artifact show for the past 3 years. There is a direct descendant of the Schreckengosts who has exhibited each year. He shows an original rifling machine and several original guns. He also has quite a lot of knowledge of the family. I believe his name is Dale Schreckengost and he lives near Putneyville.
Putneyville, by the way, is one of those Western PA towns that has "Welcome" and "You are Leaving" printed on the same sign