Early in his training, the defensive shooter learns his goal is not to kill his attacker, but to stop the threat immediately. Because all defensive handgun rounds are relatively low powered (compared to a rifle or shotgun), firing two shots to the upper chest area greatly enhances the potential for the kind of damage that will end hostilities. If the bad guy dies, that's certainly unfortunate, but the goal is to stop the attack and stop it right now.
Many years ago, Col. Jeff Cooper devised the term "double tap" to describe those two fight-stopping shots. However, Cooper nearly quit using the term toward the end of his career because it simply wasn't descriptive enough. Essentially, the delivery of two center-mass shots to the upper chest area with a pistol evolved into two different shooting techniques—the controlled pair and the hammer.
The controlled pair is the first of these techniques a defensive shooter should learn. It starts with drawing from the holster, acquiring the sight picture and delivering a center-mass shot. Then, the shooter immediately recovers from recoil, reacquires his sights and delivers a second shot to the same area as quickly as possible. There are three sight pictures involved because the shooter, following his second shot, should immediately acquire the sights again as he evaluates the target to determine if further action is necessary.
With the hammer, the shooter draws his weapon, acquires a sight picture (or at least gets his front sight on center mass) and delivers two quick shots based upon that one sight picture. Again, following the second shot, the shooter recovers from recoil, acquires the sights and gets back on target as quickly as possible.
The key to performing both techniques with speed and precision is to use the isometric grip associated with the Weaver stance. Your shooting hand pushes the handgun forward, while your support hand pulls back. The shooting arm is straight, or almost so, and the support arm is noticeably bent, with the elbow pointing directly down. In this position, the arms serve as shock absorbers. When done correctly, this technique greatly reduces a handgun's muzzle flip and the shooter is able to get back on target much faster. Having the body positioned in an aggressive combat stance also enhances one's ability to reduce the effects of muzzle flip and recoil.
Proper grip is especially important when executing the hammer. Without proper handgun control, the second shot will often be fired while the pistol's muzzle is still elevated during recoil. In that case, the shot will likely impact high or possibly even miss.
Deciding which technique to use depends upon distance to the attacker and your skill level. Extreme close-range attacks are the most deadly because everyone is a good shot in such instances. The closer the range, the more the hammer is the appropriate response. Frankly, it's not even necessary to see a complete sight picture—just make sure the front sight is indexed on target. Being the first to get off two shots and turn them into two well-placed hits is a highly desirable thing in a gunfight.
As distance increases, the controlled pair becomes the proper response. The shooter acquires a clean sight picture before delivering each shot. Only practice will tell the individual shooter the range at which he needs to begin using a controlled pair instead of a hammer.
Working from the holster, as quickly and safely as possible, increase the distance until you discover the second shot of your hammer technique isn't in center mass. That is the distance you need to begin to rely on the controlled pair. With practice you will be able to deliver a hammer from greater distances.
A common mistake many shooters make is to shoot slow enough so the pair of hits are grouped close together. Small, tight groups are great to show your friends, but in defensive training they indicate you're not shooting fast enough. Two hits delivered anywhere within an 8-inch circle—at your top speed—is the goal you should try to achieve.
Although there are a lot of important organs in the upper chest, it is possible for a bullet to travel through without impacting anything serious enough to stop the fight. As such, the second bullet, placed in essentially the same spot, may yield the same results. A second shot impacting a different area within center mass might be the one that ends the threat.
Even though we use terms like double tap, controlled pair and hammer to describe specific defensive techniques, it might not be a good idea to use them when talking to non-shooters. Double tap and hammer, especially, sound entirely too cavalier. Though we know what those terms mean, we should be concerned about how they are perceived by the general public. This is especially important when that same public happens to be sitting on a jury considering your fate. It might be much better to say, "I fired two shots at his upper chest area. I did this because my defensive handgun instructor told me it provided the best chance to make a criminal stop an attack."
The controlled pair and the hammer are important techniques for dealing with up-close-and-personal criminal attacks. As a defensive shooter, you should understand them, know the difference, and above all, practice them on a regular basis.