Double tap

A double tap or controlled pair is a shooting technique where two well-aimed shots are fired at the same target with very little time in between shots. Instruction and practice of the double-tap improves overall accuracy as shooters often do not have the gun fully extended on the first shot meaning the second of a double-tap is usually the better. The term hammer is sometimes used to describe a double tap in which the firearm's sights are not reacquired by the shooter between shots.

Origins
The origin of the double tap technique is credited to William Ewart Fairbairn and Eric Anthony Sykes, British police chiefs in Shanghai during the 1930s to overcome the limitations of full metal jacketed (FMJ) ammunition. FMJ ammunition is commonly used by militaries for feeding reliability, adherence to the Hague Convention regarding non-expanding ammunition, and improved penetration. FMJ rounds can fail to cause sufficient damage, requiring more hits and better shot placement. In Ian Dear’s book Sabotage and Subversion about British Special Operations Executive (SOE) and United States Office of Strategic Services (OSS) forces, Fairbairn is reported to have instructed SOE personnel in the double tap from 1944 to 1945 at the SOE training school directed by Fairbairn and Sykes near Arisaig in Scotland. The term "double tap" is now used to describe the broader technique of firing two rounds quickly and accurately to disable an opponent. The tactic is still used today by firearms handlers, police tactical teams, military personnel, counter-terrorist combat units, and other Special Operations Forces personnel.

Theory
In the double-tap technique, after the first round is fired, the shooter quickly reacquires the sights for a fast second shot. This skill can be practiced by firing two shots at a time, taking time between the shots to reacquire the sights. With practice, the time between shots grows shorter and shorter until it seems to the observer as if the shooter is just pulling the trigger twice very quickly.

There is a natural arc of the front sight post after the round is fired and the recoil kicks in. The soldier lets the barrel go with this arc and immediately brings the front sight post back on target and takes a second shot. The soldier does not fight the recoil. In combat, soldiers shoot until the enemy goes down. For multiple targets, each target should receive a double tap.

History
Double taps are an integral part of the El Presidente combat pistol shooting drill developed by Jeff Cooper in the 1970s and published in the January/February 1979 issue of American Handgunner. Also developed in the 1970s is the Failure Drill or Mozambique Drill, developed by Jeff Cooper student Mike Rousseau. This drill is to practice a situation where a double-tap to the torso fails to stop an attacker and so there's a third shot to the head.

The term has also been used more recently to refer to the practice of following up a drone missile strike with a second strike several minutes later.

In pop culture
Always striking or shooting zombies with a double tap is one of Columbus's rules in the movie Zombieland.

In the game Payday: The Heist, SWAT units occasionally shout "Double tap! Triple tap! Just keep tapping!" after the players have taken many hits and still stand.