Is it the gun - or the bullet - that most determines the damage?
It can be a combination of the two.
Using a relatively small, low power bullet like the 7.62x39 in a standard configuration, the damage you see is almost impossible.
The same round jazzed up though, you MIGHT come close.
A 14mm round on the other hand, in its standard configuation, could in fact do this damage and more very easily. Souped up, you could probably take off the whole head, not just a portion.
The point is, in this case, it is unlikely that the damage was caused by rifle seen in the previous photo.