What design feature of a bullet is responsible for increasing accuracy and distance?

The feature of a bullet that significantly enhances accuracy and distance is the rifling of the barrel. Rifling refers to the spiral grooves cut into the interior of the firearm's barrel. When a bullet is fired, these grooves impart a spin to the bullet as it travels down the barrel. This spin stabilizes the bullet's flight, much like how a spinning football flies straighter and further than a non-spinning one.

The stability provided by this rifled spin helps maintain a stable trajectory and reduces the impact of external forces such as wind and gravity, leading to improved accuracy over longer distances. Without proper rifling, a bullet would be more susceptible to yaw (nose up or down) and drift, which can negatively affect its accuracy and range.

Other design features such as stabilizing fins and expanding tips serve different purposes. Stabilizing fins are not commonly found on traditional bullets and are mostly seen in certain types of projectiles, while expanding tips are designed to improve terminal performance upon impact but do not contribute to the bullet's accuracy during flight. Barrelling is not a term typically associated with the design aspects of the bullet itself but rather pertains to the overall construction of the firearm’s barrel. Thus, rifling is the critical design element for ensuring