A barrel does not have parts per se. You can have sights (front and rear) on a barrel, but the barrel is usually one piece, sometimes two.
the barrel does not spin in a S&W, or any other brand of modern revolver. The part that rotates is called a cylinder, and it is turned by a piece that is called a "hand ", or a "pawl".
A barrel is part of a gun
River mouth and your mouth, Isn't it?
genus and species
The map picture