I have shot thousands upon thousands of rounds of 45 acp and I would never deer hunt with it. It just has no down range punch. About the range of a bow.

Energy does not kill a deer, damage, such as blood loss or organ failure, does. The wider a bullet is, the greater the area of the wound. Additionally, the heaver a bullet is, the further it will penetrate. Thus, a combination of large caliber and heavy weight produces a high volume wound...ie. greater damage. A 45 acp from a rifle will easily handle any deer out to 100 yds. At that distance you'll probably still have around 400 ft.lbs. of energy, but the bullet will most likely give you an exit wound with massive trauma and blood loss. The 45 acp is a real thumper, and regardless of where you aim (heart/lungs or shoulder) you should get a wound easily capable of killing a deer out to 100 yds.