Which of the following factor determines extent of wound caused by a bullet?

A bullet's ability to wound is directly related to its kinetic energy (E=mv2/2) at the moment of impact. Because kinetic energy increases in direct propoion to weight (mass) of the missile and the square of its velocity, a bullet travelling at twice the speed of a second bullet of equal weight and similar shape, possesses four times much energy or wounding power. Ref: The essentials of forensic medicine and toxicology by Dr K S Narayan Reddy, 27th edition, Page 189.