I have bought a total of three cases through various sources. Each time I bought some, another place advertised a better price! My last purchase was CMP and I do think they had the best price by just a bit. And at least the money is going to someone who is helping shooters get surplus military guns.
It is steel core, at least, that's what my kid's magnet tells me. I have only been able to shoot three en bloc clips so far but it seems accurate. At least as good as surplus M2 ball and probably a little better.