Six different prototypes were made during the XB development. Of the 6 designs, the XB6 was selected. Some parts of the XB6 resembled FN FNC such as the suppressor and sights. Further development of the XB6 evolved into the XB7 and finally the XB7C, also known as the XK2. Externally similar in appearance to the AR18, the K2 uses polymer for the forearm, pistol-grip and side-foldable buttstock. The fire control system and bolt carrier group are derived from the American M16 rifle, but few of the parts, including the bolt and carrier, are interchangeable with the M16. The gas operating system is derived from the AKM. The K2 uses the same magazine as the M16. The barrel rifling has 6 grooves, 185 mm (1-in-7.3) right hand twist. The K2 has 3 selective firing modes: semi-auto, 3-round burst, and full automatic.