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The 457 mm-long barrel, has six right-hand grooves and a 228 mm (1:9 in) twist rate. The barrel's external profile (from the breech to the front sight base) is identical to the Tantal's barrel, but the length from the foresight base has a visible tapered contour with a decreasing diameter towards the muzzle end, used to mount a flash suppressor .
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.
Some early trials versions of the M16 rifle had 1:14" twist barrels, but this was increased to 1:12" twist in early military production to improve stability with 55-grain (3.6 g) M193 lead-core bullets in the early 5.56×45mm NATO cartridges. Twist was increased to 1:9" after combat experience demonstrated the advantages of longer 62-grain (4.0 ...
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).
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
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 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 Model 0000 rifle and Model 6000 carbine use a slower 305 mm (1:12 in) twist rate for the shorter and lighter American M193 bullet. Fabrique Nationale also offers semi-automatic-only Law Enforcement carbine versions: [ citation needed ] the Model 7030 with a 178 mm (1:7 in) rifling twist and the Model 6040 with a 305 mm (1:12 in) twist rate.