The 5.56×45mm NATO is a rimless bottlenecked intermediate cartridge family developed in the late 1970s in Belgium by FN Herstal. It consists of the SS109, L110, and SS111 cartridges. On 28 October 1980, under STANAG 4172, it was standardized as the second standard service rifle cartridge for NATO forces as well as many non-NATO countries. Though they are not entirely identical, the 5.56×45mm NATO cartridge family was derived from and is dimensionally similar to the .223 Remington cartridge designed by Remington Arms in the early 1960s.
5.56×45mm NATO with measurement, left to right: Bullet, case, and complete cartridge
The 7.62×51mm NATO and 5.56×45mm NATO cartridges compared to an AA battery
Service rifle cartridge cases: (left to right) 7.62×54mmR, 7.62×51mm NATO, 7.62×39mm, 5.56×45mm NATO, 5.45×39mm
5.56×45mm NATO cartridges in a STANAG magazine
An intermediate cartridge is a rifle/carbine cartridge that has significantly greater power than a pistol cartridge but still has a reduced muzzle energy compared to fully powered cartridges, and therefore is regarded as being "intermediate" between traditional rifle and handgun cartridges.
From left to right: 9×19mm (pistol cartridge) 7.92×33mm (intermediate cartridge) 7.92×57mm (fully powered cartridge)
The Sturmgewehr 44, a development of the earlier Maschinenkarabiner 42(H)
The 10.4x38mmR Swiss is an early example of an Intermediate cartridge.
