I think the Appalachian School rifles (AKA Southern Mountain Rifles, Hog Rifles, etc) are distinctive for several reasons.
1. The NC mountain area was settled "last" in the original 13 Colonies. But once started it was settled relatively quickly, as frontiers were. Next, after the Revolution, men were given land for their service. A generation or two later a few roads were cut into the region, centered say around Hendersonville, NC. The hog road, long before a railroad. Some of those gunsmiths schooled in SC or in the NC piedmont. Other's came down the Great Wagon Road into the Yadkin valley, then moved quickly west into the mountains, bringing their skills with them.
2. The North Eastern TN region was settled somewhat before that, bringing in gunsmiths schooled up north in the Shenendoah Valley and as far as PA I suppose.
What that means is they didn't have 5 generations of making German style rifles, militia contract rifles, etc to evolve into a Long Rifle. It was a mixture of people from different schools coming in a relatively short period, but still somewhat isolated from each other. They CAME with long rifles. Then altered and adapted those designs some.
Those two regions (TN and NC) did not really mix much because of the difficulty of travel over the range. Yes, people did move over towards TN mostly, but sometimes the other way. But it was not like in the flatlands of the Atlantic colonies, with easy roads and trails and even railroads everywhere by 1855. In 1855, Western NC was pretty remote. In 1799 it was VERY remote. During the Civil War, the TN side of the range was Unionist, the NC side was a mix of Confederate and Unionist counties. Travel was extremely dangerous and hate and discontent was remembered for a generation or two after the war. So for 2-3 generations gunmaking remained the same, and didn't evolve as quickly as elsewhere.
Another reason the Appalachian rifles are distinctive was their purpose (hunting small game, shooting matchs) was different from wealthy planters down in the Piedmont, who often had the money to commission a fancy rifle with brass on it to show off to neighbors. I seriously doubt most of the Piedmont rifles were being used daily for hunting. THey were hung on the mantle or used occasionally. People in the Piedmont rode their horses or buggies to one of the hundreds of towns and bought food stuff in drygoods stores, butcher shops etc. People in Western NC had to forage, hunt, look out for bears or Indians, for at least 1 generation longer. It was a frontier, which slowly became tamer, then the Civil War happened.
Another reason is the relative scarsity of brass raw materials. Iron ore was common, every frontier settlement had a blacksmith. It's not a stretch for a blacksmith to become a gunsmith - many did.
The Appalachian School did "transition" from several regions and directions. Some coming down from PA/German influence, some from Virgina, some coming up from Charlestown, some over from Catawba. A father would make a style he had learned, like Matthew Gillespie or Peden, and some aspects would be handed down to their sons. Like the forward facing spur on the hand rail. But 1 range over, another family was making a slightly different style. Further over in Tennessee, they started making a loop ring at the end of the hand rail. 40 years later, TN rifles were still putting that loop there.
