What is the role of rifling in firearm barrels?

Rifling plays a crucial role in firearm barrels by imparting a spin to the projectile as it travels through the barrel. This is achieved through the helical grooves cut into the barrel's interior surface. When a bullet is fired, the grooves catch the bullet and cause it to rotate around its axis. This spin stabilizes the bullet during flight, leading to improved accuracy and consistency in trajectory. The gyroscopic effect created by the spin helps keep the bullet on a straighter path, reducing the influence of external factors such as wind and gravity.

The other options do not accurately describe the function of rifling. It does not primarily focus on reducing barrel weight, increasing the length of the barrel, or decreasing bullet velocity. Instead, the primary purpose of rifling is to enhance the performance of the projectile through the application of spin.