Abstract: A rifle having a rifled barrel and a cartridge having a bullet having a diameter, a length, a ballistic coefficient (BC), and a muzzle velocity (V1) greater than 1250 ft/sec are related to achieve accuracy at very long range in that the twist of the rifling is substantially equal to: 83.7 ÷ ( bullet ? ? ? length × 2 ? B ? ? C bullet ? ? diameter ) × bullet ? ? diameter × [ 1 + ( V 3 V 1 × 0.667 ) ] where: V2 is the entry speed for the transonic, i.e. 1,250 ft/sec., and V3 is V1 minus V2. A rifle barrel for receiving a bullet has rifling twist according to the relationship. A method uses the relationship to determine the rifling twist for a rifle barrel receiving a known bullet. Another method uses the relationship to design a cartridge for a known barrel rifling. The relationship is particularly applicable for bullets having a high BC, such as 0.325 or greater.