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If a 5.56×45mm NATO cartridge is loaded into a chamber intended to use .223 Remington, the bullet will be in contact with the rifling and the forcing cone is very tight. This generates a much higher pressure than .223 Remington chambers are designed for. [3] NATO chose a 178-mm (1-in-7) rifling twist rate for the 5.56×45mm NATO chambering.
The rifling twist rate for this cartridge is 177.8 mm (1 in 7 in), 6 grooves right hand twist, Ø lands = 5.56 millimetres (0.219 in), Ø grooves = 5.69 millimetres (0.224 in). [6] According to STANAG 4172 and the official NATO proofing guidelines the 5.56×45mm NATO case can handle up to 420.0 MPa (60,916 psi) piezo service pressure.
1:14: 1 right hand twist every 14 inches (356 mm) .222 Remington or .223 Remington (US M193) 1:12: 1 right hand twist every 12 inches (305 mm) .223 Remington (US M193) or 7.62×39mm; 1:10: 1 right hand twist every 10 inches (254 mm) 9×19mm NATO; 1:9: 1 right hand twist every 9 inches (229 mm) .223 Remington & 5.56×45mm NATO
The major dimensional difference between the chambers that fire the .223 Remington and the 5.56×45mm NATO is the longer and larger-diameter "freebore" [3] in the 5.56 chamber (0.0566 in (1.44 mm) vs 0.0250 in (0.64 mm) length, 0.2265 in (5.75 mm) vs 0.2240 in (5.69 mm) diameter). Freebore is a short and smooth section of the barrel that is ...
The AR-15 rifle usually comes chambered for either the military cartridge 5.56×45mm or the .223 Remington. Because of the pressures associated with the 5.56×45mm, it is not advisable to fire 5.56×45mm rounds in an AR-15 marked as .223 Remington, since this can result in damage to the rifle or injury to the shooter. [1]
Weapons designed to adequately stabilize both the M193 or SS109 projectiles (like civilian market clones) usually have a six-groove, right-hand twist, one turn in 9 inches (1:228.6 mm or 41.1 calibers) or one turn in 8 inches (1:203.2 mm or 36.5 calibers) bore, although other and 1:7 inches twist rates are available as well.
It also has the fastest rifling twist ratio for the .223 Remington of the three models(1:9 instead of 1:12). Early production rifles had a 1:12 twist rate and post-2014 rifles have the 1:9 twist rate. [2] The CZ 527 Varmint in .223 has muzzle velocities for standard-load 45-grain (2.9 g) ammunition of around 3,500 feet per second (1,100 m/s).
The .223 WSSM was introduced in 2003 by the Browning Arms Company, Winchester Ammunition, and Winchester Repeating Arms Company. The .223 designation is a reference to the popular .223 Remington. It is currently the fastest production .22 caliber round in the world with muzzle velocities as high as 4,600 feet per second (1,402 meters per second).