The bi-metal 7.62x39 (AK-47) bullet doesn't have a copper jacket.
As with most of the Russian military and commercial ammo, the jacket is mild steel with a thin copper wash plating to prevent rust, over a lead core.
This copper coating is very thin and can be easily scraped off as the OP has indicated.
If you recover a 7.62x39 steel bullet at the range you'll find the copper plating is largely gone from the rifling and friction in the bore.
Only commercial type bullets in the 7.62x39 have a real copper jacket over a lead core, and most of those are American made bullets.