modern way to accessorize the K2 and K1 is to mount a now (limited) standard issue PVS-4K Rail Integration System. It consists of an aluminum body with a long, uninterrupted rail for optical/red-dot and night-vision sights and three other rails located on the bottom and both sides. The rails are of the Picatinny-type. Despite the shortest handguard ever seen on any assault rifles, the K2C variants have had issues with overheating, and thus most of the K2's around the world are the original K2, with the barrel mostly exposed, unlike the K2C. The K2 is also able to accept a brass catcher basket, as the South Korean army requires its soldiers to pick up and return empty cartridge cases after training sessions, both for financial reasons (the brass cases are recyclable) and for security reasons, as the soldier must prove he or she has actually expended the issued ammunition. This minimizes the risk of a soldier keeping unauthorized live ammunition which could be used in criminal activities. K1 and K2 weapons systems When personnel from the South Korean army special command were invited to see the XB-series prototypes, they requested the development of a new submachine gun to quickly replace a series of different weapons in their use. With no time to develop a new weapon, ADD made one based on the XB rifle prototypes called XB-S (short). It used a direct impingement gas tube rather than a piston to achieve the required short length, which was faster to make since they had short-barrel CAR-15 designs to work off of and no time to redesign a new short gas piston. The barrel used 1:12 inch rifling to fire M193 rounds, as during its development there were no plans to adopt SS109 ammunition in the South Korean army. The shortened design was adopted as the K1A SMG in 1981 and issued to special forces, commanders, radio operators, and others who needed a short SMG-like weapon. While the K1A SMG is commonly regarded as an SMG version of the K2, the K1 is a separate weapon altogether. The primary differences between the two weapons include: development time and intent (the K1 took less time to develop and entered service sooner than the K2, and was developed originally as a submachine gun because it was intended to replace the M3 Grease Gun; the K2 was developed from the start as a service rifle);