I agree with nub. It sounds like the deer was quartering to you and you either pulled the shot off or didn't actually have the crosshairs on his chest. The slug probably hit about the last rib and came out his underside area knocking out the white hairs. No deer with a 12 guage slug directly through the chest from the front is going far. He is probably dead by now and he may not have gone far from the last place you had a trail.