The K-12 is chambered in 7.62x39mm M43. Designed for militaries who want an AR15 platform but want to use the cheap and plentiful amunition of the AK-47 and AKM platform. using modified AK magazines that cut there ammunition capacity to 27 rounds instead of 30. The prototype (XK-12) was the first version but it was too expensive for to mass produce for countries who needed cheaper weapons.
The K-12 was the final version using the same magazines but using the M16A1 platform.