After the Dallas fire at an indoor range, the steel core I could understand. Also rifle and big mag ammo limitations are probably to protect the backboards on the indoor range.
Yep, their rules specifically state the steel core ammo is a fire hazard, and the limitation on caliber is to preserve their backstop (and prevent shoot through).
On a side note, I saw a guy there last week shooting, and every round was sparking off the floor. As I was leaving, I mentioned it to one of the guys behind the counter. He mentioned something about, "He said it wasn't Russian ammo." Then grabbed eyes, ears and a magnet. Sure enough, steel ammo, and they kicked the guy out. He was mad, and kept insisting his ammo wasn't steel core. But the round hanging off the end of the magnet, by the bullet, kinda proved him wrong. He said he was never coming back and he'd tell his friends not to go there. The reply was priceless:
"Don't let the door hit ya, where the Good Lord split ya!"
For the record, this range is almost always packed...one guy and his friends won't make a lick of difference.