To enhance the domestic appeal, S&T Motiv developed the K2A, which retains the full-length K2's features (including bayonet lug) while utilizing the upgrades of K2C including the upper receiver/handguard Picatinny rail, M4-style adjustable stock. Later, it was renamed K2C1 (C="Exterior design changed without performance improvements", by the South Korean Defense Specification) and adopted by ROK forces. K2C1 had several changes compared to K2A, including a new extended handguard rail with optional lower/side pictinny rail sections, flattop upper receiver with a detachable rear backup sight, and a new Magpul CTR-like adjustable stock. As of 2016, 200,000 K2C1s are in service with frontline troops. Partially due to the rail's screw attachment method, the K2C1 is slightly heavier than the original model. ( vs. ) Design 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. The K2 can be equipped with the DPI K201, an undercarried 40×46mm single shot grenade launcher patterned after the American M203. The Republic of Korea Armed Forces originally planned to replace the entire K2 with new S&T Daewoo K11 dual-barrel air-burst weapon. However, high cost and skepticism over the effective firepower of the 20mm grenade led to the decision to provide 2 K11s to each squad, keeping 2 grenadiers as well. Consequently, the standard 9-person infantry squad of the Republic of Korea Armed Forces is currently equipped with 2 K2 rifles, 2 K2 rifles with K201 grenade launcher, 2 K11 DAWs, 1 K3 light machine gun, and the rest with either K1 or K2. The K2 is also sometimes used with bipods and 4× magnification scopes, in a role similar to the Designated Marksman Rifle. A more