Fair point. Unfortunately I doubt some ranges who have blanket no steel core rules, will care for the technical nuances. They will just use the magnet and say "not allowed".
Sure, I agree. They don't care. Same rules on my indoor range at Colby Shooting Club. Just magnet decides. However, it's good to know for ourselves that, in reality, there is lead in the bullet and the small steel core (soft steel) is sheathed in it.