the spiral grooves on the inside of a gun's barrel that cause a projectile to rotate when it is fired, or the action or process of making such grooves;
e.g. The firearm has unique rifling in a style that is no longer used.
(verb)
making a system of spiral grooves on the inside of a gun's barrel in order to make the bullet rotate when it is fired, making it more accurate over long distances;
e.g. The machine is used for rifling the gun with great precision.