That looks to be a miss print. I believe it should be a 5.6x50R Mag a round developed by Heym to meet certain power requirements for hunting in Europe. I comes in rimmed and rimless version and uses a .224 bullet vs the .227/.228 bullet in the 5.6x52R. It looks very much like an extended 222 Rem Mag and the rimless version uses the same .378 bolt face as the 223 Rem and 222 Rem Mag. Here in the states it make a great predator hunting round, I use it in a V. Bernardelli Combo gun.
5.6x50R in the Bernardelli getting the job done. Just north of our southern border.
Just south of out northern border
Wish I had a BRNO in the 5.6x50R, missed one in an auction a few years back but the 5.6x52R works well also. Another southern coyote.