what box do i need ?

Ed

If you are referring to the MTM plastic ammo boxes - the same one for a 7.62x39.
http://www.mtmcase-gard.com/caliber/ammo-box-762x39.html

thanks now to see who stocks them.

Ed

If you plan on loading ammo that is longer than the "factory" 7.62x39 or Grendel length, pay attention to the height of the box. A lot of boxes won't accept long-loaded ammo.

The Frankford boxes are taller if you are loading long.