Some years ago I watched a documentary about archery. The really good bow hunters gave a fine accounting of themselves. Then, switch to Mongolia and the descendants of the Mongols. These guys lived with their bow. They would race around on horses and hit, every time, targets like apples, balls, etc, from running and rearing horses with their short, stiff bows.
And guys like Bob Munden hitting an egg at 100 yards with a .45 acp 1911; and that's just starting his accomplishments. So many of the old legendary shots are suspect and could easily be a product of luck. But if one has talent and lives with his weapon, upon which his and his family's survival depends, it's easy to see that there is a rarefied level of skill that we'll never know.
Charles Chenevix-Trench, in
A History of Marksmanship, Mongol (or Turkish) archery from moving horses, and if my memory serves me correctly remarks that hitting an orange from a moving horse at ten or fifteen yards or so, while not exactly
easy, is not nearly as difficult as it sounds - he was one of the last British cavalrymen to train on horses, right before his regiment was mechanized, and by the end of his training he was doing similar feats with a revolver. MacDonald Hastings, in
How to Shoot Straight, while mostly devoted to teaching the Churchill method of shotgunning, does have a chapter on snap-shooting with a rifle in which he mentions Boers hitting antelope on the run from the saddle of a moving horse, apparently a common feat for them. There is also the story of the guy along the Ohio frontier, whose name I have forgotten, killing the Shawnee "Old Clubfoot" with a snapshot at 100 yards through the woods while on the back of a moving horse - Eckert mentions the incident in both
The Frontiersmen and
That Dark and Bloody River, I think.
So, I think that someone who grew up along the frontier or in the backcountry with a rifle in their hands was, as you say, very skilled within the parameters of normal (for them) weapons use, and probably capable of feats that to us would be quite extraordinary. The caveat is that snapshooting is a quite different skill-set than long-range shooting, and since I doubt that most riflemen did much shooting beyond 100 yards or so outside of fighting Regulars, trying to shoot a man at two or three times the range would have taken them outside their comfort zone.
Like Flehto, I'm very curious as to how they managed to get an accurate load without the aid of a shortstarter, particularly since I'm not wholly convinced that they coned either, at least as we understand the term. I have a suspicion that the answer is quite simple and obvious, but the differences between modern replicas in such things as crowning, twist, and sights, as well the differences in how the guns were/are used, are obscuring something.