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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.
The M16A2 rifle, which is designed to fire the 5.56×45mm NATO SS109 ball and L110 tracer bullets, has a 1 in 7-inch (18 cm) or 32 calibers twist. Civilian AR-15 rifles are commonly found with 1 in 12 inches (30 cm) or 54.8 calibers for older rifles and 1 in 9 inches (23 cm) or 41.1 calibers for most newer rifles, although some are made with 1 ...
This allows gas to blow by, and loosens the hold of the bullet on the barrel. An increasing twist, however, will make the rifling become wider than the grooves in the bullet, maintaining the seal. When a rifled-barrel blank is selected for a gun, the higher-twist end is located at the muzzle.
Conventional eight groove rifling on the left, and octagonal polygonal rifling on the right. Polygonal rifling (/ p ə ˈ l ɪ ɡ ə n əl / pə-LIG-ə-nəl) is a type of gun barrel rifling where the traditional sharp-edged "lands and grooves" are replaced by less pronounced "hills and valleys", so the barrel bore has a polygonal (usually hexagonal or octagonal) cross-sectional profile.
Historically, this table has been referred to as a "drop table." The drop table can be generated empirically using data taken by the shooter at a rifle range; calculated using a ballistic simulator; or is provided by the rifle/cartridge manufacturer. The drop values are measured or calculated assuming the rifle has been zeroed at a specific range.
Another attempt at building a ballistic calculator is the model presented in 1980 by Dr. Arthur J. Pejsa. [18] Dr. Pejsa claims on his website that his method was consistently capable of predicting (supersonic) rifle bullet trajectories within 2.5 mm (0.1 in) and bullet velocities within 0.3 m/s (1 ft/s) out to 914 m (1,000 yd) in theory. [19]
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The 6.5mm Creedmoor designated as 6.5 Creedmoor by SAAMI, and as 6,5 Creedmoor by the C.I.P. [4] is a centerfire rifle cartridge introduced by Hornady in 2007. [6]It was developed by Hornady senior ballistics scientist Dave Emary in partnership with Dennis DeMille, the vice-president of product development at Creedmoor Sports, hence the name.