Gary, you dog, I think you knew what a can of worms you were opening.
Dan, Tim, everyone, what you're missing is this. Wallace has been researching what he calls the "backcountry rifle culture" for a number of years now. This culture is what many call the Scots-Irish, few of which were Irish, and many of which weren't Scots! From about 1717 to 1775 there was a hugh influx of these people who disembarked at ports along the Delaware and migrated down the Great Wagon Road (more or less I-81 down the Valley of Virginia). Over several hundred years these people, who lived in a much contested area including the north of England, the south of Scotland, and Northern Ireland, developed a "warrior ethic". They became natural fighters, much like some of the Indians here.
They brought this warrior ethic with them to America. Here they adopted the "short" rifle of the Germans, who had preceded them by a few years down the Wagon Road through Pennsylvania, Maryland, and the Shenenoah Valley. Having trouble loading the short rifle with its patched ball when mounted, these warriors asked the German gunsmiths to lengthen the barrel to that of the common fowler, about 3 1/2 feet or so. This way they could set the butt on the grown as they rammed the patched ball down the bore. The backcountry horses were much smaller than common pleasure horses today.
Sure, Wallace is speculating about the longrifle and the pouch/horn issue, but he's doing so from the mindset that a people with a warrior ethic settled the Valley of Virginia. Men who quickly adapted to the dangers involved.
For more info on this backcountry people, read Albion's Seed by Fischer.
For more info on why the rifle was an important part of this culture, badger Wallace into finishing his book!!
Andy
BTW- I think Wallace wears his pouch on the right and horn on the left.