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Miller twist rule is a mathematical formula derived by American physical chemist and historian of science Donald G. Miller (1927-2012) to determine the rate of twist to apply to a given bullet to provide optimum stability using a rifled barrel. [1]
Early production rifles had a 1:12 twist rate and post-2014 rifles have the 1:9 twist rate. [2] The CZ 527 Varmint in .223 has muzzle velocities for standard-load 45-grain (2.9 g) ammunition of around 3,500 feet per second (1,100 m/s). The 1:9 barrel twist in the Varmint Kevlar reduces muzzle velocities by about 1.5%.
Rifling of a 105 mm Royal Ordnance L7 tank gun Conventional rifling of a 90 mm M75 cannon (production year 1891, Austria-Hungary) Rifling in a GAU-8 autocannon. Rifling is the term for helical grooves machined into the internal surface of a firearms's barrel for imparting a spin to a projectile to improve its aerodynamic stability and accuracy.
The data are all for barrels with a twist rate of 1 turn in 10 inches (250 mm) which is needed to stabilize the heaviest bullets. The higher muzzle velocities reported by Nosler for 165 grains (10.7 g) and heavier bullets use loads employing a slow-burning, double-base powder (Alliant Reloder 22).
The overall case length after the shortening and re-sizing is 1.565". The cartridge was designed to use .308" diameter bullets in weights of 110 to 150 grains, with a standard twist rate of 1-12". [1] Wilson Combat states that heavier bullets can be used in a barrel with a 1-8" twist rate for subsonic loads. [4]
The only major difference between the 601 and 602 is the switch from the original four grooves, right-hand 1:14-inch (1:355.6 mm or 64 calibers) rifling twist rate to the more common four grooves, right-hand 1:12-inch (1:304.8 mm or 54.8 calibers) twist. This was done as the original 1:14-inch twist rate to just stabilize the 55 grain bullet ...
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Its noise levels are similar to those generated by .22 LR match ammunition. The weapon is fitted with a special .308 Winchester/7.62×51mm NATO 406 mm (16 in) long barrel which has a twist rate of 229 mm (1 in 9 in) and an integral suppressor. The aluminum alloy integral suppressor is fitted over the barrel and can be removed by the user.