I agree, but there are some misunderstandings about the time period.I would not call it “mythology”.
First it's NOT that the cost of lead and powder in Europe was much less than in America. It was true, however, that the availability and cost of lead and powder in Frontier areas, where the big game hunters were being supplied, was higher there than in a colonial trading hub like Boston, New York City, Charleston SC. The more shots one could get from a pound of lead and pound of powder = more efficient use of funds, for the Long Hunters who were hide hunters, as well as for the market hunters, the subsistence hunters, etc.
The caliber of the rifles shrank over time in the East, as the length of the barrels increased. This seems to correlate with the presence of large, dangerous game, and the lack thereof. Conical bullets such as a Picket, Sugarloaf, and Minnie Balls slowly began to appear as early as the 1830's but seem to have been more for target work, than hunting. The Minnie didn't get popular until the 1850's due to the Crimean War, but was poo poo'd for large, dangerous game by hunters, who preferred the patched round ball (See Forsyth The Sporting Rifle and Its Projectiles)
The Germanic gun makers that immigrated to The Colonies were accustomed to shorter, large caliber, rifled pieces. However, they were quite well acquainted with what we would call a "long rifle", as in Germany these were popular for target shooting. The "jaeger" was better suited for hunting from horseback, in rather thick underbrush, in forests that were not "old growth" because of the millennia old need for charcoal. The Forests of what today is France, Germany, Austria, and Poland were very similar to a lot of forest one finds today in the USA. When the hunters were here in old growth forests with huge trees, and a triple canopy that reduced underbrush, they often dismounted and hunted afoot, and needing rifles very precise in accuracy, caused the lengthening of the barrels, while economics reduced the calibers. One may dispatch a black bear with a single .54 round ball..., and it wasn't until later that "loading for bear" traditionally in the East meant to add powder AND a second patched ball, not a conical, into the smaller caliber rifle of the day.
While it's true many if not all true gunsmiths in the colonies were capable of making a rifle of any caliber, the question was more of were they able to make multiple calibers and twist rates? Knowing how to construct a machine to rifle a barrel by hand was one thing, but having the TIME and RESOURCES to create the machine to be able to rifle a raw barrel to that specific caliber and twist rate is another matter. Some gunsmiths used just one machine for most if not all of their rifling. See the Hawken Brothers of St. Louis MO, originally hailing from Hagerstown, MD.
LD