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Arguably, the criticisms about range, accuracy, and lethality are related to the change in barrel length and twist between the M16 and M4. The earlier 5.56 rounds (the original M193) were optimized for a 20-inch (51 cm) barrel with a 1:12 twist. In 1980 STANAG 4172 defined the 5.56×45mm NATO chambering and its accompanying 1:7 twist rifling. [38]
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]
Government-specified barrel profile increased to between 0.675 and 0.575 inches; A2: Also referred to as the "government" or "gov't" profile. Barrel profile for which the portion of the barrel in front of handguards is thickened to 0.715 inches; HBAR: A barrel that in some portion is thicker than government-profile, usually underneath the ...
The Ruger AR-556 is a semiautomatic AR-15 style rifle manufactured by U.S. firearms company Sturm, Ruger & Co. Introduced in 2014 as an entry-level AR-15 using a direct impingement action, with variants since being released such as the upgraded AR-556 MPR (multi-purpose rifle) in 2017 [1] and the AR-556 pistol in 2019.
The rest of the barrel was maintained at the original thickness to enable the M203 grenade launcher to be attached. 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 barrel has a chrome-lined bore with 6 right-hand grooves and a 178 mm (1:7 in) rifling twist rate that is optimized for use with heavier SS109 5.56×45mm NATO rounds. A barrel with a 305 mm (1:12 in) twist rate designed specifically to stabilize the lightweight M193 cartridge is also available. [2]
The Ranch Rifle is a basic model offered in a wood or synthetic rifle stock paired with a blued or stainless steel receiver and a standard 18.5" tapered barrel (1:9" RH twist rate). These rifles feature an adjustable ghost ring rear sight and winged front sight, and they are sold with a detachable Picatinny scope rail mount and a choice of two ...
Although, both shorter 16-inch (410 mm) carbine barrels and longer 24-inch (610 mm) target barrels are also available. Early models had barrels with a 1:12 rate of twist for the original .223 Remington, 55-grain (3.6 g) bullets. Current models have barrels with a 1:9 or 1:7 twist rate for the 5.56×45mm NATO, 62-grain (4.0 g) bullets.