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The FN-created cartridge was named "5.56×45mm NATO" with a military designation of SS109 in NATO and M855 in the U.S. [13] These new SS109 ball cartridges required a 228 mm (1-in-9 inch) twist rate while adequately stabilizing the longer L110 tracer projectile required an even faster, 178 mm (1-in-7 inch), twist rate. [5]
The above proof round pressure requirements for the 9 mm and 12.7 mm rounds established by the British Ministry of Defence are higher than the current (2008) C.I.P. proof round pressure requirement legislation for the civilian equivalent 9 mm Parabellum (C.I.P. P max rating 235 MPA / (34,083 psi) and .50 Browning (C.I.P. P max rating 370 MPA ...
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 table below gives a list of firearms that can fire the 5.56×45mm NATO cartridge, first developed and used in the late 1970s for the M16 rifle, which to date, is the most widely produced weapon in this caliber. [1] Not all countries that use weapons chambered in this caliber are in NATO. This table is sortable for every column.
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 SEAL Recon Rifle (nicknamed the "Sniper M4" [2] and "Recce" [3]) is an American designated marksman rifle and assault rifle used by the United States Navy SEALs.Essentially a heavily modified M16 rifle, it is intended to provide SEAL snipers and designated marksmen with a versatile, accurate, lightweight, and relatively compact weapon chambered in 5.56×45mm NATO.
5.56×45mm NATO: Caliber: 5.56 mm (.223 in) Rate of fire: 950 round/min: Effective firing range: 500 meters, depends on barrel length: Maximum firing range: 850 meters, depends on barrel length: Feed system: STANAG magazine: Sights: Iron sights or various optics
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 ...