A Smooth rifle has both a barrel and Stock that are shaped as you would a rifle. Some even carry rear sights.
By contrast, fowlers, and muskets are different. Fowlers have shotgun shaped stocks, and thinner barrels- often half octagon, half round, but not always. Fowlers will tend to be the lightest,a nd best balanced, of the various smoothbores, because they were designed for civilian- not military- use.They were intended to be used to shoot flying birds, as well as an occasional turkey on the ground, and Deer.
Muskets tend to have Round Barrels, and the straight military style stocks, that are thicker in the wrist, and butt than you usually will find on Smoothrifles, or Rifles, for that matter. Muskets were almost strictly military weapons, built for strength, so that they tend to weigh much more than the typical fowler.
The only thing that Muskets, Smoothrifles, and Fowlers have in common is that they are smoothbores, at least until the early 1800s, when "rifled Muskets" came into fashion just before the change from Flintlock to Percussion action took place in military arms. Few "smoothrifles" began life as smoothbores. Rather they were often rifles that had been shot out, and were then bored out to a smoothbore to give the owner further use from the older firearm.
I hope this helps you understand the differences. :hmm: :thumbsup: