That's the point, it CAN'T do that.
How many of these close up human head shot have you done to be able to say for sure?
I'm not so sure.
I know for a fact that a 7.62x37 will go clean through 1/4 inch steel plate at 50 yards. (I have personally put many of these rounds through many steel plates with my SKS)
One has to do a hydrostatic force calculation to determine if the shock from a 7.62x39 fired from 2 meters would create enough explosive pressure to cause a skull to disintegrate from the lower orbital lobe up.