I once had an original smooth rifle made near Norristown, PA around 1810 to 1820. It was exactly like a rifle, but without rifling. Thicker barrel wall than a smoothbore (trade gun)or a fowler. In my mind a smooth rifle has heavy barrel wall thickness like a rifle, a trade gun type smoothbore was for shot , buck or ball and had barrel wall thicknesses of about 1/8 inch at the muzzle. Fowlers were strictly for shot and often had very thin barrel walls at the muzzle, sometimes as thin as stove pipe. I'e seen examples of all three. Folwers tend to have plain shaped butt stocks, some times fish bellied. Trade gun smoothies, also have very plainly shaped stocks. Smooth rifle stocks have the same characteristics as rifle stocks with roman noses, crescent butts, cheek pieces, and often cast off. (cast off is the butt being angles slightly away from the centerline to accomodate the shooters cheek and to better get the eye in line with the sights. )