1 shot drops are a myth, handguns don't have the energy that a rifle does to knock a man off his feet.
there have been reports of police shooting people 20 times before they die.http://www.fbi.gov/publications/leb/2004/oct2004/oct04leb.htm#page_15
"In the authors’ ongoing study of violence against law enforcement officers, they have examined several cases where officers used large-caliber hand guns with limited effect displayed by the offenders. In one case, the subject attacked the officer with a knife. The officer shot the individual four times in the chest; then, his weapon malfunctioned. The offender continued to walk toward the officer. After the officer cleared his weapon, he fired again and struck the subject in the chest. Only then did the offender drop the knife. This individual was hit five times with 230-grain, .45-caliber hollow-point ammunition and never fell to the ground. The offender later stated, “The wounds felt like bee stings.”
In another case, officers fired six .40-caliber, hollow-point rounds at a subject who pointed a gun at them. Each of the six rounds hit the individual with no visible effect. The seventh round severed his spinal cord, and the offender fell to the ground, dropping his weapon. This entire firefight was captured by several officers’ in-car video cameras."