Charlie I agree whole heartedly, there is no way he hit that buck straight on with a 12 gauge slug in the chest, as you stated, even if the slug did not directly contact lungs/heart/arteries, the shock would have turned them into mush. He either gutshot him or he hit the shoulder and tore it up! If he gut shot it, its dead, if he did hit it in the shoulder straight on it is probably dead also, but I have seen more than one deer recover from being shot in the ham or shoulder, usually though they have one heck of a limp, I have also seen 3 legged deer.