I know an old timer who attempted to put a hole throug a leaf of spring steel from a D-9 Cat. After breaking all his bits, he propped it against a log, set up a table, put some sandbags up, set a .30-06 on them, tied a string to the trigger, stood behind a tree, and when he pulled the string, the bullet hit the steel and bouncedd back and mushroomed the barrel of the rifle.