5.56

HK MR556A1 556MM HK416 RIFLE 5.56mm NATO 223REM. Available in California from Cordelia Gun Exchange!

The 5.56 or 5.56×45mm NATO

The 5.56 or 5.56×45mm NATO is a rimless bottlenecked intermediate cartridge family developed in the late 1970s in Belgium by FN Herstal.
Some of the military and tactical rifles chambered in the 5.56 cartridge are the M-16 and AR15, M4, HK MR556, IWI Tavor, and the FN SCAR 16:

HK MR556A1 556MM HK416 RIFLE 5.56mm NATO 223REM. Available in California from Cordelia Gun Exchange!

California legal Tan IWI TAVOR X95 5.56mm 223REM FDE Bullpup Rifle. Available from Cordelia Gun Exchange.

California legal Tan IWI TAVOR X95 5.56mm 223REM FDE Bullpup Rifle. Available from Cordelia Gun Exchange.
California legal Featureless FN SCAR 16S 5.56 FDE RIFLE with stock block. Available from Cordelia Gun Exchange.

California legal Featureless FN SCAR 16S 5.56 FDE RIFLE

California legal Featureless FN SCAR 16S 5.56 FDE RIFLE with stock block. Available from Cordelia Gun Exchange.

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, SS110, 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. The 5.56×45mm NATO cartridge family was derived from, but is not identical to, the .223 Remington cartridge designed by Remington Arms in the early 1960s.

5.56 -Wikipedia