This question needs a little expansion to properly address the issue. First, handguns have three kinds of actions (methods for firing): single action (SA), Double Action (DA) and Double Action Only (DAO). Single action handguns are made ready to fire by cocking the hammer or striker manually. This action must be repeated for every shot. The cowboy guns of the Old West were single action. SA handguns tend to require much less force on the trigger to drop the hammer. Double Action handguns can be made ready to fire either by manually cocking the hammer or by pulling the trigger if the hammer is down. DA handguns require much more force to pull the trigger if the hammer is down since the trigger is connected to the hammer in some way and must raise the hammer before it will fire. Example: Smith & Wesson Model 10 revolver. Double Action Only refers to a handgun whose hammer or striker is cocked only when the trigger is pulled. There is no other way for the user to cock the weapon. Trigger pulls require the same force as a DA handgun when the hammer is down. DAO has become popular with firearm makers who want to avoid lawsuits from negligent discharges. Since it can take 10 pounds of pressure on the trigger to fire the weapon, the user would be hard pressed to say the "gun just went off when I barely touched the trigger". Example: Smith & Wesson SW9VE 9mm pistol. A decocker is a lever on the side of a semiautomatic pistol that allows the user to drop the hammer without firing the pistol. When the lever is moved, a physical block is put between the hammer and the firing pin as the hammer is released. The decocker does not prevent the weapon from being fired if the trigger is pulled. Not all pistols have a decocker. On many pistols, the lever is just a safety and prevents the hammer from falling if the trigger is pulled. A manual safety is a device that must be conciously engaged to prevent a weapon from firing. The lever on the side of a Colt M1911A1 pistol that is just in front of the hammer is a manual safety. If it is not engaged, the pistol will fire if the trigger is pulled. Example: Any M1911A1-style pistol

Decocking means the hammer is no longer cocked and in its rearmost position when thus lever is pushed. It eases down to its frontal position. Many double-action semi-automatic pistols have this decocking type of safety lever. To fire such a pistol, you must give the trigger a long double-action pull or pull back the hammer with your thumb to cock it for ingle-action fire. Single-action semi-auto pistols have a manual safety that blocks the gun from shooting until this safety is released. Many men carry such pistols with the hammer cocked and this safety engaged. Of course the decocker is a different type of manual safety. DAO means Double-Action Only. Such a pistol can only be fired by a long and heavy trigger pull. This prevents top accuracy. I do not see any good reason why DAO pistols should be made. They are popular only because the media promotes them. The media deceives people on all levels of life. It tells them what to do, say, think and buy. Much of the stuff media tells us is deceitful. Gun magazines recommend DAO pistols because the makes of such junk pay them much in advertising. One of my ex boyfriends showed me a copy of "Guns & Ammo" magazine that had two articles mentioning DAO pistols. Wiley Clapp wrote that a DAO pistol is the best one for everyone. Combat shooting champion Bill Wilson said he had no use for DAO pistols. My lover agreed with Bill Wilson. It is irrational to remove an option that allows much greater accuracy. Why do it at all? .