What design feature in firearms increases accuracy and distance by causing a bullet to spiral?

Rifling is the correct answer because it refers to the spiral grooves cut or formed into the interior of a firearm's barrel. These grooves cause the bullet to spin as it is propelled forward when fired. This stabilizing spin helps to maintain the bullet's trajectory, increasing both accuracy and effective range. The aerodynamic effect of the spin ensures that the bullet can travel further and more accurately, rather than tumbling in flight.

Other options, while they may influence firearm performance in different ways, do not serve the primary function of inducing spin on the projectile. For example, grooving might refer to any pattern that does not necessarily stabilize a bullet in the same way rifling does, barrel sizing refers to the diameter of the barrel, which can affect fit but not spin, and barrel porting involves the modification of a barrel to reduce recoil and muzzle rise but does not help with the accuracy related to bullet spin.