northmn,
it may also indicate that as we got closer to the industrial revolution, balistics became more scientific and more generally known. the result was longer barrels to more efficiently use the burn rate of blackpowder in those small calibers. as the calibers got smaller as compared to the earlier guns, pressures went up and it was dicovered that the barrels had to built heavier to handle it. hence, the deeply crescented butt plates and the "across the chest, arm mounted short pulls,.... maybe an adaption of the scheutzen style of target shooting, with thier hooked butts, just not so exagerated for everyday use. the guns were shot off-hand as well as from a convenient rest...yree branch or what-ever while hunting. the deep crescent in the buttplate made a very good anchor to hold up the front of the gun.....in close to the armpit where you have lots of leverage against it's weight. as barrels improved and got smaller and lighter, that style of shooting was abandoned in favor of today's more framiliar open stance. even the planes rifles had the deep butts and lots of drop, made to be shot off-hand as thier barrels were purposely heavy because of the powerfull loads thay needed to handle. on the other hand, the military practiced the more conventional by modern standards , "open-stance", because it had the advantage of honest-to-goodness scientific methodology to produce guns that were not so heavily barreled and could be shot in an open stance more comfortably, as well as the connection to the advanced european industries and military that were"cutting edge" in firearms devopement at the time.
earlier guns with thier larger bores, pressures weren't as much of a problem. i think allot of what we today think was scientificly derived was arrived upon impericly.... small, independant builders started paring weight off the barrels by swamping them 'till they started blowing up and then backed off on the swamp untill it stopped, or examples were obtained from europe and copied. i doubt that the majority of the early builders, save a few, had any formal education in metalurgy and balistics. they just had the talent, skills and work ethics to build guns. it would be real interesting to learn the curriculum of an apprenticeship in a gun shop from the late 18 to early 19th. centuries. by the early 19th. century, as gun components became mass produced and thier availability became less timely, they relied on the industry's reasearch to supply safe components, so barrels got lighter and the open stance more common. prior to this, as the trend towards smaller bores developed and pressures went up, barrels started blowing and the swamp was eliminated and so the vicious circle went on in favor of more iron as a safety factor. most of those small builders were just good skilled craftsmen living in a world of slow communication and little formal scientific education.
by the advent of the ind. revolution, barrels were made pretty much the same as the are now, with exception of today's alloys, of course. earlier, not truely knowing how strong the iron was they were using for thier barrels, it was prudent to over build it for safety's sake.