An indigenous rifle program started in 1972. Initial requirements were for prototypes to be chambered in 7.62×51mm NATO as it was the only standardized ammunition for Western Bloc. Prototypes XB-1 through XB-5 were akin to AR-15-series rifles with some exterior changes; designers attempted to use as many M16 components as possible to save time and money, such as the direct gas impingement operation, sights, and handguards. In 1975, the XB-6 prototype with long-stroke gas piston was created, and converted into 5.56×45mm NATO chambered XB-7 in 1977.