I think, based on some of the research links posted earlier, it is hard to come up with a simulation of the hog head. If you can't get one from a hunter or a slaughterhouse, maybe you can compare pellets using a more uniform, hard material like masonite or something like that. It may tell you which pellet is better but you won't know if it is good enough.
I think a phone book, wet or dry, should be a good place to start. You get to see the difference between measuring from entrance to the back of the skirt vs depth of the nose of the pellet. I think you will find that usually a heavy pellet will have a shallower hole to the back of the skirt, in a dense medium like wood, but you have to cut it to see the actual depth of the nose. Using a phone book, you can count the pages easily.
Perhaps hanging the rifle from a rope as a Ballistics Pendulum would be educational?.... It would certainly be entertaining....