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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]
The barrel rifling was revised to a faster 1:7 (178 mm) twist rate to adequately stabilize the new 5.56×45mm NATO SS109/M855 ball and L110/M856 tracer ammunition. The heavier longer SS109/M855 bullet reduced muzzle velocity from 3,260 ft/s (994 m/s), to about 3,110 ft/s (948 m/s) [ 195 ]
The standard bullet diameter for 6 mm caliber cartridges is .243 inches (6.2 mm), the same diameter used in the .243 Winchester and 6mm Remington cartridges. 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 ...
Bullet drop and wind drift are shown both in mil and moa. The 7.62×51mm NATO has a 3.38 mL (52.0 gr H 2 O) cartridge case capacity. The exterior shape of the case was designed to promote reliable case feeding and extraction in bolt-action rifles and machine guns alike, under extreme conditions.
Another issue that has an effect on the barrel's hold on the bullet is the rifling. When the bullet is fired, it is forced into the rifling, which cuts or "engraves" the surface of the bullet. If the rifling is a constant twist, then the rifling rides in the grooves engraved in the bullet, and everything is secure and sealed.
The Aguila SubSonic Sniper round uses a .22 short case with a 60-grain (3.9 g) bullet (twice the weight of the .22 short bullet and 50% heavier than a .22 long rifle bullet) giving an overall length of a .22 long rifle round, making categorizing the SSS problematic: while the SSS case size is .22 short, the firing chamber of the barrel must be ...
A gain twist has a slow initial twist in the barrel, progressively getting faster until the final twist rate is attained near the muzzle, resulting in less torque being imparted to the bullet during the highest stress phase of the interior ballistic cycle, and thus less wear in the throat of the barrel. Gain twist was phased out in the last ...
The bore twist is 1-turn-in-11.25 inches [1:285.75 mm] and the rifling is five radial lands and grooves (5-R) with a right-hand (RH) twist. Because of the odd number of lands, none of the lands are 180° apart, i.e. in direct opposition. This results in less bullet deformation, which (at least in theory) produces more consistent point of impact.