The K2 is capable of firing a rimless bottlenecked intermediate cartridge derived from what cartridge?
Daewoo Precision Industries K2:  Shoulder-fired and gas-operated, the K2 is capable of firing both 5.56×45mm NATO and .223 Remington ammunition. 5.56×45mm NATO: The 5.56×45mm NATO (official NATO nomenclature 5.56 NATO) is a rimless bottlenecked intermediate cartridge family developed in Belgium by FN Herstal. 5.56×45mm NATO:  It is derived from, but is not identical to, the .223 Remington cartridge.
.223 Remington