I was there as well. It was insane. It was endless mag dump after mag dump. Splits were about .75-1.50, for 30 rounds at a time.
Muzzle flash? More like muzzle flamethrower. It was cartoon-like.
Fortunately the range gods smiled upon me, as I was far away at the end working with a new shooter. Had I been where Jconn was, I'm certain I wouldn't have gotten anything done.
This was by far the worst disruptive noise incident I have ever experienced at a range.