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In firearms, rifling is the helical groove pattern that is machined into the internal (bore) surface of a gun's barrel, for the purpose of exerting torque and thus imparting a spin to a projectile around its longitudinal axis during shooting. This spin serves to gyroscopically stabilize the projectile by conservation of angular momentum, improving its aerodynamic stability and accuracy over smoothbore designs.

This picture, taken in 2016, shows the conventional rifling of an Austro-Hungarian 90 mm (3.5 in) M75 cannon, manufactured in 1891, on display at Ljubljana Castle in Slovenia.Photograph cr: Petar Milošević

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