Why are barrels rifled?

Barrels are rifled to stabilize the bullet in flight. The process of rifling involves cutting helical grooves into the barrel's interior surface. This design imparts a spin to the bullet as it is fired, which is crucial for maintaining its trajectory and accuracy over distance.

When a bullet spins, it experiences gyroscopic stability, which makes it less susceptible to the effects of wind and gravitational drop. This stabilizing effect helps ensure that the bullet flies true to its intended target. In contrast, a non-rifled barrel would lead to a less stable flight path, potentially resulting in a decreased accuracy.

The other options relate to different characteristics of a firearm but do not explain the primary purpose of rifling. While rifled barrels can impact bullet speed and may have an indirect effect on issues like muzzle flash, these are not the primary reasons for rifling. The design does not contribute to increasing ammunition capacity either, as that is more related to the firearm's magazine and chamber design.