Rock River has come out with an AR in 7.62x39mm. Most well-studied AR gunsmiths know that the AK round has a taper that doesn’t function well with the AR magazine design.

So, some bright spark at RRA went :

Thereifixedit.

The lower takes an AK mag. Of course, it means you’re stuck with the AK “rock-n-lock” reload, but you have to give a little to get a little.