Having seen 34 Shreckengost rifles to date, this John McCann signed Shreckengost is the most ornate rifle of them all with perhaps the exception of Wm and Lincoln's personal rifle, yet even it is unengraved. My conclusion is that this rifle was made for a man of both means/status and a man
who has the opportunity to travel and buy a custom rifle from a man out of his area.
It makes sense from many perspectives. According to the Beers History of Armstrong County, Wm Shreckengost was known as the best maker of muzzleloading rifles in the U.S. in his time.
I had originally believed this to say John McCown, but after a closer inspection by a friend with experience, I believe it says McCann.