As I understand whats been explained about the physics involved in that "trick" most of the concussive force is lost as it travels through the rock. BUT, I bet he was'nt expecting it to rebound and bank off his face. LOL! and OUCH!
You stand out from the crowd my friend. Your good with most cars (we'll leave your'* outta this since you are caught up to me on motors) and do a lot to help the community. Most barbarians keep to themselves when they aren't dragging some woman or a fresh kill into their cave.