Looking at the shot placement on that buck anyway, I would bet there was less then a couple ounces of meat damage on that buck.
As I always say, being over gunned is a mythical situation as long as you put the bullet on the right spot.
From what we have heard from some out there, I am surpised the 300 gr SMK penetrated at all!!! Please read that with a bit of sarcasm!!! LOL
Congrats and tell that American hero congrats and thank you!!!