Search results
Results From The WOW.Com Content Network
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.
NATO chose a 178-mm (1-in-7) rifling twist rate for the 5.56×45mm NATO chambering. The SS109/M855 5.56×45mm NATO ball cartridge requires a 228 mm (1-in-9) twist rate, while adequately stabilizing the longer NATO L110/M856 5.56×45mm NATO tracer projectile requires an even faster 178 mm (1-in-7) twist rate.
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 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 heavier longer SS109/M855 bullet reduced muzzle velocity from 3,260 ft/s (994 m/s), to about 3,110 ft/s (948 m/s) [ 195 ]
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.
Initial design focused on optimal performance with supersonic bullets in the 85-115 gr (5.5-7.5 g) class, therefore a 1:11 twist rate barrel with 5R rifling was selected. Subsequent consumer interest in firing "heavy-for-caliber" subsonic bullets led to the design, testing, and production of 1:7 twist barrels to stabilize the longer heavier ...
By intentionally choosing a slow twist rate the 55 grain bullet used in the 5.56 Ball M193 cartridge was only just stable in flight. The damage caused by the 5.56 mm bullet was originally believed to be caused by instantaneous "tumbling" on impact and render a wide, incapacitating wound due to the slow 1 in 14-inch (360 mm) rifling twist rate.
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 ]