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Thus the optimum rate of twist for this bullet should be approximately 12 inches per turn. The typical twist of .30-06 caliber rifle barrels is 10 inches per turn, accommodating heavier bullets than in this example. A different twist rate often helps explain why some bullets work better in certain rifles when fired under similar conditions.
Also, the newer methodology proposed by Dr. Arthur Pejsa and the use of the G7 model used by Mr. Bryan Litz, ballistic engineer for Berger Bullets, LLC for calculating boat tailed spitzer rifle bullet trajectories and 6 Dof model based software have improved the prediction of flat-fire trajectories. [9] [55] [56]
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.
A very-low-drag bullet (VLD) is primarily a small arms ballistics development of the 1980s–1990s, driven by the design objective of bullets with higher degrees of accuracy and kinetic efficiency, especially at extended ranges.
This ballistic trajectory is referred to as the bullet path. If the projectile is spin stabilized, aerodynamic forces will also predictably arc the trajectory slightly to the right, if the rifling employs "right-hand twist." Some barrels are cut with left-hand twist, and the bullet will arc to the left, as a result.
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). Early .257 Weatherby rifles has a twist rate of 1 revolution in 12 in (300 mm) but all current rifles are manufactured with a twist rate of 1 revolution in 10 in (250 mm).
The 160 gr (10 g) bullet which has a sectional density of 0.328 is similar in sectional density to a 220 gr (14 g) .308 caliber (7.62 mm) bullet. As sectional density plays a large factor in penetration, the .264 caliber (6.5 mm), though a diminutive caliber from a North American point of view, has had excellent results in the field.
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 ...