Tueller Drill

One of the classic lessons in nearly all self defense courses the reactionary gap concept. This is the critical time lapse between an attacker without a gun and the time it takes to effectively stop them with a handgun.  One of the pioneers on this topic was Dennis Tueller was a Salt Lake City Police academy trainer.  In March of 2008, Dennis wrote an article entitled "How Cloase is Too Close?" which was published in SWAT magazine in March of 1983.  

Over the years, this concept has been called many things like the 21 Foot Rule, The Tueller Principle, Reactionary Gap, Danger Zone, and many more.  The misconception many people take from the drill is that there is a definite distance that makes it legal to use deadly force against an attacker.  This is not true.  The first problem is that there is no such thing as a typical attack.  There are too man variables to apply "rules" of time or distance.  A totality of the circumstances may include time and distance, but you will also need to consider things like available cover, terrain, footing, lighting, number of attackers, bystanders, obstacles and any number of other variables.  The intent of the Tueller Drill is to demonstrate that the relative time for an attacker to cover 21' is similar to the time an average trained concealed carrier can draw and fire a couple shots on target. It was never intended to establish a definite 21' radius that would allow the use of a firearm against any perceived threat.

Dr. Bill Lewenski, a consultant at the Police Policy Studies Council, has also done extensive research in the field of reaction response time.  He has used high-speed photography to do elaborate studies to support these concepts.

Many use of force experts such as Massad Ayoob and Manny Kapelsohn have also contributed and supported the concepts set forth by Dennis Tueller.