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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.
The C.I.P. recommends that commencement of rifling begin at 8.97 mm (0.353 in). Bore diameter is given as 12.55 mm (0.494 in) and groove diameter is 12.80 mm (0.504 in). The C.I.P. recommends a five groove barrel contour with each groove having an arc length of 5.33 mm (0.210 in) and a twist rate of one revolution in 406 mm (16.0 in).
Both, the U.S. Army's M24 Sniper Weapon System and U.S. Marine Corps' M40 sniper rifles are built from the Remington Model 700 rifle with different degrees of modification. The main difference being the custom fitted heavy contour barrel and action length.
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).
While standard rifle barrels taper from breech to muzzle, high precision rifles will often use a barrel with far less taper, called a heavy barrel, sometimes leaving the barrel cylindrical all the way to the muzzle, called a bull barrel. Either technique greatly increases the stiffness of the barrel by enlarging the average diameter, but this ...
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.
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 is cold hammerforged and is available in two different contours (fluted light, or smooth semi-heavy) and comes in lengths of 510 and 610 mm (20 and 24 in). [6] The muzzle threading is 5 ⁄ 8-24 UNEF (3A tolerance class). [6] The stock, outside of the chassis, is made from high impact-resistant fiber-reinforced polymer. [3]