Nothing wrong with using a 7.62 mag in a AKS-74u. Plenty of 3rd party AKS-74us chambered to the 7.62 round, the side folding Yugo M92 comes to mind. It's not suprising considering the AK is a open sourced gun. Look around the internet there are plenty of AK chambered to all sorts of calibres and mix of parts. See Kyber Pass AK for more details.
But purist would cringe at people still calling a AKMSU, AKS-74u or Krinkov a AKS-74u. It's like calling a Mac 11 an uzi.
__________________
|