I am going to resurrect this fantastic thread, because I am in the process of building (having built) a flintlock British Sporting Rifle, which to most blackpowder folk looks like a "Hawken" going backwards.
Because I have owned and hunted with British black powder rifles for a while, I have spent a silly amount of time trying to piece together the history of the British "Best" gun trade in a way that explains the evolution of their incredible sporting rifles. Donald Dallas wrote the definitive "British Sporting Rifle and Gun," which has photos of early flintlock half stocks as well as the later percussion versions that became the sine qua non of the sporting world. Qualities that many American BP shooters seem to think of as distinctly American were in fact developed in Britain, before coming ashore here and evolving into the Pennsylvania Long Rifle and the Hawken/ Plains Rifle.
So when we see a flintlock Hawken-style rifle that raises eyebrows nowadays, we have only to look at the sporting rifles made in England, Scotland, and Ireland from 1770s-1860s to understand that these later forms and designs were not uniquely American. From what I can tell, and what I believe happened, the Hawken brothers exactly copied the pre-existing British Sporting Rifle that was so incredibly popular across the British empire at that time, but they exchanged a much heavier and more rugged barrel for the highly swamped and more delicate barrel found on the British rifles. I am not saying the British were effete and weak, or that their guns were too svelte for the American frontier. Anyone reading Sir Samuel Baker's adventures knows he took his British Sporting Rifles into battle with the world's most dangerous beasts for many decades, and both he and the guns (that didn't get stepped on by elephants) all came out relatively unscathed and functioning for many years under harsh conditions. But the truth is that the American free trapper frontiersman might have to occasionally swing his rifle like a bat or a club if he was going to keep his scalp, and only the slightly tapered heavy barrel of a "Hawken" would put up with that.
Other than the barrel and the arced butt, when I look at a Hawken/ Plains Rifle, I see a British Sporting Rifle adapted to our own needs and conditions here in America. There is an understandable tendency to look at American gun making as beginning in eastern Pennsylvania and never looking back. We see this in some of the BPCR books, where the otherwise distinguished authors greatly puzzle and even agonize over where oh where did the 45-120 or the 50-130 cartridges ever come from...without realizing the 45-120 Sharps is the British .450 Black Powder Express, and the 50-130 Sharps is the British .500 Black Powder Express, both of which pre-dated the Sharps, but which were adapted to American guns. The point being that a great deal of what we Americans proudly consider to be our own native talent and ingenuity, i.e. PA Long Rifles (evolved from German jaegers) and especially the Hawken/ Plains Rifle (almost exactly copied from the British Sporting Rifle), actually came from Europe.
That said, I am a proud American, and while I believe in international trade, I won't go too far, and so I consider Europe in all ways (guns, politics, cars) to be the prototype and America to be the finely finished end product.