I think there is some commingling of technology, application and terminology occurring in the thread.
In the late 1700s and early 1800s "rifles" were regarded as bing highly accurate, but were not considered suitable for the tactics of the era due to their slower rate of reloading, particularly after they have been fired more than 10 or so shots.
Getting a tightly patched ball down a badly fouled rifled bore can be a real challenge, and doing it quickly is unlikely. In contrast, you can continue to load un-patched round balls down a smooth bore, due to the reduced fouling and the greater clearances involved.
In essence, it's a choice between accurate, aimed fire and a large volume of fire. Given that the tactics of the day were predicated on ranks of soldiers facing each other at ranges of 80-100 yards, volume of fire prevailed. Consequently, the smooth bore musket remained the premier infantry weapon long after the rifle came into common use for hunting, sniping, etc.
What changed the equation was the minie ball, a conical projectile with substantially more weight than a round ball with a hollow base expanding skirt that allowed the projectile to be undersized so that it could be easily and quickly load in a fouled rifled bore. On firing, the skirt expanded to grip the rifling, and the rings in the base helped clean the bore minimizing to some extent the accumulation of fouling in the rifling.
The end result was that a longer, heavier projectile could be fired in a smaller caliber barrel with loading nearly as fast as with a smoothbore musket, but with the accuracy expected from a rifle. Thus in the US, you saw a shift from .69 caliber "smooth bore muskets" to .58 caliber "rifled muskets". Both types retained the same general features of the "musket" design, with the major difference being the presence of the rifled barrel.
In US service the smooth bore 1840 and 1842 muskets, while they pre-dated the minie ball, were designed with a barrel thick enough to accommodate rifling at some point, as even at that point there were experiments with various projectiles that would expand in a rifled bore during ramming, or firing. Eventually, many 1842 rifled muskets were rifled to accommodate a .69 caliber minie ball.
Ordinance tests however determined the .58 caliber minie ball was much more accurate than a .69 caliber minie ball, and that the .69 caliber minie was so heavy that it made the recoil problematic for many soldiers, further degrading accuracy.
In any event, by the time the American Civil War / War of Northern Aggression rolled around, you had troops in the field with substantial numbers of .58 caliber and .69 caliber rifled muskets that were capable of delivering effective aimed fire at ranges far greater than the 80-100 yard ranges that were common at the time.
The end results were devastating with the minie ball inflicting about 90% of the total casualties in the civil war, and doing incredible damage shattering limbs, and doing far more damage than the rounds balls used in the past.
The saving graces at the time, were the tendencies for troops to still either final to use the sights or to aim high, and the smoke created by masses of troop using black powder weapons. Realistically speaking, when you put a few hundred people on one side facing a few hundred people on the other side, and have them all fire black powder weapons, much of the visibility disappears after the first couple of volleys, unless you have a fair amount of wind that will continually clear it away. The limited visibility tended to negate the potential advantages of the rifled musket, at least when the wind wasn't blowing.
By the end of the Civil War, we had a preview of what WWI would look like in terms of extended sieges and trench warfare brought on by the far greater range and accuracy of the rifled musket, as well as with early models of the Gatling gun - two items that made survival above ground level difficult with large standing armies facing each other over contested ground.
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While we're on the subject, if you have a well made 1860 Army replica you may have noticed that the sights (notch in the hammer with a fixed front sight) are regulated impossibly high at a normal shooting distance of 15-25 yards, but they are however well regulated for shooting at people standing 80-100 yards away, reflecting the tactics of the day.