'''5.56x45mm NATO''' is a type of [[ammunition]] for firearms. It is classified as a <span style="color:#AA0000">'''(R)'''</span>ifle caliber.
Before 5.56 NATOAt first, there was '''.223 Remington''', a civilian varmint hunting cartridge of identical dimensions which was originally designed for the Armalite AR-15, a semi-automatic rifle which gave birth to the [[Maze Customs|AR-15 platform]] and all related firearms. This cartridge formed the basis for the military cartridge that became known as '''5.56x45mm NATO'''.
Despite differences in real life between the two cartridges (namely that 5.56 NATO is rated to develop roughly 13% more pressure than .223 Rem, therefore making it ''potentially unsafe'' to fire 5.56 in .223 Rem firearms), as far as the game is concerned they are not significant enough to merit including both cartridges separately. It is considered that ''Reduced Velocity''-brand 5.56x45mm NATO ammunition in the Mazes is roughly equivalent to .223 Remington.