UCo,
I believe you that the head didn' t open ON THE OUTSIDE.......I know first hand because I got one of those " Bullet Wound" entry holes one time when I used one.

However upon examining the vital organs the Lungs had a perfect 3 blade slice thru them and a full width exit hole. I' d bet that' s exactly what happened to the deer you speak of.

That blade retention system is what scares me.........too much energy to open it and the possibility of marginal hit with no exit AND a bullet hole entrance spells TROUBLE for me.