My thought, especially after comparing the rapid fire from the video you linked above, was that it sounded more like a modified AR-15 than an AK-47. The AK's seem to have a much "tinnier" clink to them. But that's just from comparing the videos, not from any "hands on" experience...
modified AR-15 (starts around 2:30 seconds in):
AK-47 (starts around 20 seconds in):