Its a little more than 1/4" thick. It is what is left of a target that used to be used for sighters for some DCM matches at the range I was told. It no longer hangs up anywhere, but is rather proped up between two targets.
The Barnes took out about a 2 sq in chunk, and the NAB hit a little higher and took out another piece due to the cracks the Barnes made. The metal appears brittle, but the SMKs won't do anything more than nickel size craters.
A 708 with 120 gr Hornadys leave only lead splatter. I'll try to get some pictures next time I go out there.