The AK-47u is an SMG.
No, it's not.The AK-74 fires a 5.54x39mm rifle round, god damn it Call of Duty. They see a gun with a skeletal under-folding stock and they assume it's a sub machine gun.

The solid stock makes it a rifle hurr
It's just a smaller Kalashnikov model that replaced the larger AK-47/AKM 7.62 models due to it retaining stopping power but being lighter weight and lower recoil.
Let me explain this:
AK: Automatic Kalashnikov
S: Folding stock
74: Model 1974
U: Shortened carbine variant
Hence an AKS-74 would be a AK-74 with synthetic furniture, and a AK-74u would be a '74 with an under-folding stock.