Hi,
You are right, several books were written about this topic and if you are serious about the subject, read the books. A good place to start, but that has been updated over the years, is Kindig's "Thoughts on the Kentucky Rifle in its Golden Age". These kinds of online discussions frequently stray off a logical path because folks often are loose with terms and dates. What is early? What is late? Moreover, a lot of unsupported speculation often is added in as fact, and facts are often expressed as sound bites despite the fact that the true answers are much more complicated. Before the AWI, most of the rifle gunsmiths of whom we know anything, were 1st generation European (largely Germanic) immigrants or their sons. It is logical to assume they were steeped in European gunmaking traditions and methods, including decoration. As years progressed through the AWI and later, and home grown generations took over, those connections faded to some degree. Wide buttstocks, robust design, and larger bores were European traditions and their influence on long rifles was strong at first but faded over time. Europeans often made guns with long barrels, even rifles, so the advantages of that feature were known. I believe the short barrels on Germanic flintlock rifles was a carry over from the cheek stock used on Germanic wheellock rifles during the 16th - early 18th centuries. Cheek stocks were not tucked into the shoulder, they were simply held against the cheek so a short barrel might handle better than a long heavy one. However, in contrast, the Silesian tschinkes were relatively long barreled and small-bored wheellock rifles with cheek stocks, so there were exceptions. With respect to economies of powder and lead, and ballistics of long barrels, all that likely was known to European gunsmiths and I am sure powder was scarce during the AWI but there is no documentation of which I am aware that clearly states why long barrels and smaller bores became the norm in America. A plausible argument could be made that after the AWI and into the early 19th century, small bores became common not because they were more economical on the frontiers but back on the old farms there were no deer left to hunt. The forests were gone. Small game and target shooting was all that was left. Anyway, there are some very good long rifle scholars on this forum and I am sure they will chime in.
dave