Part of how much accuracy you can expect was mentioned as to whether they have sights, as in smooth rifles, and also to some extent the differences in ignition. My Brown Bess was a very reliable weapon, it had a large lock that set off a very impressive shower of sparks and worked well with 2f priming. It was also very slow. Many of the Fowler's had finer locks and faster ignition. Two types of accuracy, the accuracy of the weapon and ability of the shooter. Some weapons were made rather difficult to shoot. The Natives for instance complained that the NW Gun was too straight and originals were found with carved out stocks to compensate. Some exact repos today are also made that way.
In the great lakes area a military unit was developed during the French and Indian war whose techniques are still studied today by special forces. Roger Rangers never used a rifle. Their loads, according to my sources, were buck shot, buck and ball, and ball. They also had swivel guns mounted on the York boats that were loaded with shot to discourage any Natives from coming out in canoes to attack them.
According to one price list I saw a smoothbore would cost about $5.00 and a rifle about $15.00. A factor also to consider is that the rifles were physically heavy weapons. Another is that a rifle is a specialized weapon and best used in skilled hands. We have today, probably better shots than existed in the frontier, as we have the ability to shoot more. I grew up on a BB gun then a 22 before going to a larger rifle. That just was not available back then. Also comparatively speaking, ammunition is much cheaper today so we shoot more. When I shot bullseye competition, I really only shot against about 4-5 other shooters. There might be over 30 registered, but most were not competitive. At 100 yards some had trouble hitting the paper. (No smoothbore would have stood up in that competition, as it would not have had the accuracy) My point is that in many cases it wouldn't matter much to some users if the gun were rifled or not as they just could not shoot that well. If ranges are close most smoothbores were lighter in weight to lug around and worked as well. As an example, one of the proportions I read for a trade rifle was a 50 cal 35 inch 1 3/16 inch barrel. I would definitely want a horse to carry that one with. On a final note many of the shot charges were not all that heavy, some as light as one half ounce, equivalent to a 54 RB. As I mentioned the 410 was real popular for grouse when I was younger for pot shooting them in the head, often out of a car. As to the shot sizes, that likely varied. Most of my references stated that shot was more or less home made. Real fine shot was not popular in the earlier days like today. Hinton claimed that #3 was popular for ducks in the late 1800's.
DP