I started a new thread following this one as the side effect I do object on is so unusual I thought it deseved an own topic:
I convinced the owner of that Hungarian headstamped 7.62x51 to pull the projectile so we can examine it closer.
It turned out that the projectile used is an Impala hunting projectile:
The odd thing now is that the projectile is made of solid brass (a friend confirmed that from the factory). Nevertheless the projectile IS magnetic!
Not as magnetic as solid steel (actually only iron, cobalt and nickel are magnetic) but still magnetic enough to be attracted by a strong magnet.
The question is now if the brass alloy used is containing nickel as I think the two other materials can be ruled out.
Any thoughts on that or did somebody observe this before?
Here an image (no photoshop or cheat!):