What design feature causes a bullet to spiral for increased accuracy?

Rifling is the design feature that causes a bullet to spiral, which significantly enhances its accuracy. rifling consists of helical grooves cut or pressed into the interior of the barrel of a firearm. These grooves impart a spin to the bullet as it travels down the barrel when fired. The spin stabilizes the bullet's flight path, allowing it to maintain a straighter trajectory and reducing the effect of external factors such as wind or gravity. This increased stability results in improved accuracy over longer distances.

Other options, such as grooving, might sound similar but are not the specific design intended for stabilizing projectiles. Crowning refers to the finishing of the muzzle end of the barrel to ensure that the bullet exits smoothly, while threading is typically associated with attaching suppressors or other muzzle devices, and does not contribute to the bullet's accuracy in flight.