This is a special 30 06 round made for US wound ballistic test. I wonder if somebody has some closer informations. A wooden sabbot holds an steel ball. These balls where used in two different sizes.
The idea was to break down human size to small animals like cats and dogs and reduce the ammo in the same way. Then the test animals get test shots.
The steel balls shouldt also copy steel fragments from shells.
Here is the very interesting site with lots of information handling leathality, enemy weapons and shell fragmentation ect…
The very cruel site of ammunition.