.270 is a high velocity round. You need to match the bullet to the game. Same for many of the .30 cal guns. There is such a thing as overkill in this regard.

My guess is your bullet passed through both lungs without expending much of it's energy or expansion, basically punching a very small hole in both sides and the lungs.

Match the bullet so it expands inside the deer making a bigger and bigger hole on the way through.