The obvious suggestion here, which everyone is probably thinking, is why not contact the seller again and ask him how he arrived at the Isaac Sherill attribution, since he is the one with that knowledge, rather than anyone on this board.
Jerry Noble & Tom Moore, in their "Gun Trade In America" compendium on American gunmakers, gathered all known names from all significant sources to assemble their book. They have the following two entries:
1) "Sherill, Isaac - Burke Co., NC, fullstock percussion rifle. Source: Ed Dorr." [no info provided on who Ed Dorr was/is]
2) "Sheril, Franklin, Jackson, Jacob, Iredell Co., NC, all possible gunsmiths around 1850" Source: Bivens; Whisker et al
"Gunsmiths of the Carolinas." [note - I did not find this reference in Bivins]
The Whisker source above has two conflicting entries, i.e. same man with different first name/initial:
1) "Sherril, A. (1800- ) 1850 Iredell Co., NC. In his shop were his sons Franklin, Jackson and Jacob, listed as 'laborers.' " US Census
2) "Sherril, Hiram (1811- ) 1850 Iredell Co., NC. In his shop were his sons Franklin, Jackson and Jacob, listed as 'laborers.' " US Census
Whisker illustrated an A. Sherrell full-stocked flintlock rifle, p.156, very different from the "attributed" rifle we are discussing. Unfortunately Whisker did not state if the rifle was signed or attributed by its owner. Whisker often accepted the owner's statement on who made a rifle at face value without more details. In this case, since it has an initial with last name, I would suspect the barrel was signed that way, since attributions usually have the full name... to make them look more official.
IF, IF, IF ... this rifle is made by Isaac Sherrill of Sherrill's Ford, then the man would most likely be Isaac Sherrill, b. Aug.1781 at Sherrills Ford, NC, and died Sept 1856 at Sherrills Ford, Catawba Co., NC. Sherrills Ford started out in Rowan Co., became part of a couple other counties as new ones were formed, and ended up in today's Catawba Co. The only reference to this man's occupation is in the 1850 census. That year he was living in Iredell Co., NC [ note it is the same county as the above reference to Hiram/A. Sherrill above], was 69 years old and listed as a "farmer." I could find no reference to his being a gunsmith, although at times other gunsmiths were listed as farmers when they owned a farm of significant value. This Isaac Sherrill had parents Moses and Martha Osborn Sherrill, and married Mary "Polly" Hibbits on July 22, 1835, in Catawba Co. Isaac died at Sherrills Ford, Catawba Co., NC in Sept. of 1856 and is buried in the Sherrill Family Cemetery at Sherrills Ford.
I would lean toward a NC origin for this interesting rifle, whether made by a Sherrill or another gunsmith, based on its stock architecture, and one small detail. The lower butt molding is a double line terminated under the guard with a small "S" figure. That double line with a small, "wavy" S figure is very similar to how the Bryan gunsmiths of Rowan Co., NC, did their lower butt moldings, which were carried into central Kentucky and seen in the Lexington School rifles by the Bryans and related gunmakers. While the S is standing in this case, rather than horizonal as on Bryan rifles, it remains very similar in overall design, and I have never seen that detail on a TN rifle.
Shelby Gallien