aks74u uses 5.45 in firearm community
It takes ak 74 magazines, best match would be bakelite magazine.
AKSU is a American bastardize ak47 w/ aks74u which use ak47 magazine
For airsoft either will work as long as it aint the new marui recoil engine mags. I prefer AKS74U to use AK74 bakelite, but thats my preference.