SS109

5.56×45mm NATO
5.56×45mm NATO with measurement, left to right: projectile, empty case, complete round with projectile in case
Type	Rifle
Place of origin	Belgium
Service history
In service	1977–present
Used by	NATO
Specifications
Parent case	.223 Remington
Case type	Rimless tapered, bottleneck
Bullet diameter	5.70 mm (0.224 in)
Neck diameter	6.43 mm (0.253 in)
Shoulder diameter	9.00 mm (0.354 in)
Base diameter	9.58 mm (0.377 in)
Rim diameter	9.60 mm (0.378 in)
Rim thickness	1.14 mm (0.045 in)
Case length	44.70 mm (1.760 in)
Overall length	57.40 mm (2.260 in)
Case capacity	1.85 cm3 (28.5 gr H2O)
Rifling twist	178 mm or 229 mm (1 in 7 in)
Primer type	Small rifle
Maximum pressure (EPVAT)	430.00 MPa (62,366 psi)
Maximum pressure (SCATP 5.56)	380.00 MPa (55,114 psi)
Ballistic performance
Bullet mass/type Velocity Energy 4 g (62 gr) SS109 FMJBT 940 m/s (3,100 ft/s) 1,767 J (1,303 ft·lbf) 4.1 g (63 gr) DM11 FMJBT 936 m/s (3,070 ft/s) 1,796 J (1,325 ft·lbf) 4.1 g (63 gr) GP 90 FMJBT 905 m/s (2,970 ft/s) 1,679 J (1,238 ft·lbf) 4 g (62 gr) M855A1 FMJBT 960 m/s (3,100 ft/s) 1,843 J (1,359 ft·lbf)
Test barrel length: 508 mm (20.0 in) Source(s): NATO EPVAT testing, QuickLOAD, SAAMI, C.I.P.

The 5.56×45mm NATO (official NATO nomenclature 5.56 NATO) is an intermediate cartridge family developed in Belgium by FN Herstal. It consists of the SS109, SS110, and SS111 cartridges. Under STANAG 4172, it is a standard cartridge for NATO forces as well as many non-NATO countries. It is derived from, but is not identical to, the .223 Remington cartridge.

In the 1953, the 7.62×51mm NATO rifle cartridge was selected as the first standard NATO rifle cartridge. At the time of selection, there had been criticism that the 7.62×51mm NATO was too powerful for lightweight modern service rifles, causing excessive recoil, and that as a result it did not allow for sufficient automatic rate of fire from hand-held weapons in modern combat.

The British had extensive evidence with their own experimentation with intermediate cartridges since 1945 and were on the point of adopting a .280 inch (7 mm) cartridge when the selection of the 7.62×51mm NATO was made. The FN company had also been involved in the development of the .280 round including developing a version of the FN FAL in .280. The concerns about recoil and effectiveness were effectively overruled by the US within NATO, and the other NATO nations accepted that standardization was more important at the time than selection of the ideal cartridge.

1957: The development of the cartridge which eventually became the .223 Remington (from which 5.56mm NATO will eventually be developed) is intrinsically linked to the development of a new lightweight combat rifle. The cartridge and rifle were developed as one unit by Fairchild Industries, Remington Arms, and several engineers working toward a goal developed by US Continental Army Command (CONARC). Early development work begins in 1957. A project to create a Small Caliber High Velocity (SCHV) firearm is created. Eugene Stoner of Armalite is invited to scale down the AR10 (7.62mm) design. Winchester is also invited to participate. The parameters which are requested by Conarc are: