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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]
At its introduction the rifle came with a 24-inch barrel and was chambered for a variety of rounds such as .25-20 Winchester, .32-20 Winchester, .38-40, and .44-40. Variants in other chamberings remain in production today. [1] Even though both are lever-action rifles and named similarly, the Marlin 1894 is different from the Winchester Model 1894.
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.
To obtain maximum accuracy, bullet weight and form are matched to the rifling twist rate of the barrel. Typically, 68 gr (4.41 g) bullets are used in barrels with twist rates of 1 in 13 inch (1 in 330 mm), while 1 in 15 inch (1 in 380 mm) barrel twists can accommodate lighter 58 or 60 gr (3.76 or 3.89 g) accurately.
The M1917's barrel had a 1 in 10 in (254 mm) twist rate and retained the 5-groove left hand twist Enfield-type rifling of the P14, in contrast to the 4-groove right hand twist rifling of the M1903 Springfield and other US designed arms. The M1917 had a long 26-inch heavyweight barrel compared to the lighter 24-inch barrel of the M1903 Springfield.
SAAMI recommends a barrel rifling contour of 6 grooves with a bore Ø of .2505 in (6.36 mm) and a groove Ø of .257 in (6.5 mm) with each groove being .098 in (2.5 mm) wide. The recommended optional twist rate is one revolution in 10 in (250 mm). Both SAAMI and Weatherby recommend a freebore of .378 in (9.6 mm).
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Before the barrel can release the bullet in a consistent manner, it must grip the bullet in a consistent manner. The part of the barrel between where the bullet exits the cartridge, and engages the rifling, is called the "throat", and the length of the throat is the freebore. In some firearms, the freebore is zero as the act of chambering the ...