How did rifling improve the accuracy of firearms?

Rifling improves the accuracy of firearms by cutting shallow spiral grooves into the interior of the barrel, known as the bore.1

In traditional smoothbore muskets, projectiles had to fit loosely in the barrel to allow for rapid loading, which caused them to wobble during discharge and resulted in erratic flight. Rifling addresses this by imparting a gyroscopic spin to the projectile as it travels through the barrel. This spin stabilizes the projectile in flight, significantly increasing both range and accuracy compared to smoothbore weapons.2341

While early rifled weapons were difficult to load because the projectile had to fit the grooves tightly, innovations such as the Minié ball—a conical bullet with a hollow base that expands upon firing to engage the rifling—eventually allowed for high accuracy without sacrificing loading speed. By minimizing the tumbling and erratic movement associated with smoothbore projectiles, rifling transformed the effectiveness of infantry weapons and artillery.134