Wasn't there a ban of imported "cheap" steel core ammo...
Let me look that back up.

Be right back......

EDIT:
As I understand it -The "problem" - 1994 Steel-Core Importation Ban"
Most surplus 7.62x39 was steel core making it armor piercing ammo that was outlawed and since the steel core supply is drying up people are also depleting the lead core supply.