In order to allow cheaper and simpler training of troops, the South African Defense Forces adopted a .22 rimfire conversion kit for their R4 rifles. The system was developed by an engineer named Willie Klotz working for Thor Engineering. It is an open-bolt firing system which is quite complex, and interestingly uses the sear of the Galil/AK fire control system to fire rather than the hammer. The conversion is rather tricky to install, and in practice often required hand-fitting each kit to a specific rifle.