Inless you have the bullet in your hand, you don't know if it mushroomed...The faster a bullet is travelling the faster it mushrooms the more internal damage it makes and the faster it slows down...

The problem is, once it slows down it will not make as large of an exit hole, it will simply punch through the hide...The hide on the off side actually acts like a catcher's mitt...It expands out and stops many bullets that have slowed down and mushroomed...

Where that deer was shot you wouldn't have had a blood trail even if hit with say a 150gr Nosler Partation from a 30-06...

You'll have a higher percentage of exits and blood trails if you are hunting from a tree stand and hitting them about 4 inches above the bottom of the chest...

That bullet actually did a good job it killed the deer and did enogh internal damage that it fell within a hundred yards of the hit...