Smoothbore - History of Firearms and Rifling

History of Firearms and Rifling

Early firearms had smooth barrels, and fired projectiles with no significant spin. These projectiles had to have stable shapes, such as finned arrows or spheres, to minimize tumbling during flight. However, spherical bullets do tend to rotate randomly during flight, and the Magnus effect means that even a relatively smooth sphere will curve when rotating on any axis not parallel to the direction of travel (see knuckleball for an example of intentional random tumbling.)

A rifled barrel, having spiral grooves or polygonal rifling, imparts a spin to the projectile which stabilizes it and prevents it from tumbling. This does two things; first, it increases the accuracy of the projectile by eliminating the random drift due to the Magnus effect, and second, it allows a longer, heavier bullet to be fired from the same caliber barrel, increasing range and power (see external ballistics). In the eighteenth century, the standard infantry arm was the smoothbore musket; by the nineteenth century, rifled barrels became the norm, increasing the power and range of the infantry weapon significantly.