There are four types of actions around which semi-auto pistols are built. It’s important to understand the differences:
Single Action – 1911 Colt .45 ACP, Browning Hi-Power 9mm, CZ-75B SA
This is the oldest autoloader design still in service, designed by John Browning (with the help of the Army Ordnance Board) during the period between 1905 and 1911. The hammer must be cocked, generally by racking the slide, for the gun to fire. This design in 1911 .45 ACP is favored by competitive shooters, FBI SWAT, LPD SWAT, FBI Hostage Rescue Team, and many special forces units because it has the best trigger and outstanding accuracy. For the gun to be carried in a state of readiness, the hammer must be cocked and the manual safety applied, “cocked and locked” (see “The Conditions of Readiness“). This looks scary and is not recommended for novices or those suffering from attention deficit disorder.
Double Action/Single Action – Beretta 92F (Armed Forces M9), most Smith & Wesson autos, Walthers, Walther P99, and some Rugers.
This has been the standard design for most autos for the last 50 years. These pistols are cocked by the first trigger pull, but subsequent shots are cocked by the action of the slide cycling back. Consequently, the first trigger pull is long and harder (Double Action) since it is also cocking the hammer. Subsequent trigger pulls are easy (Single Action) since the hammer is already cocked. These guns have an external safety lever which puts the gun on safe and de-cocks the hammer. This is generally thought to be the safest design since the long, heavy first trigger pull and the external safety which blocks the firing pin tend to prevent the gun from going off by accident. The criticism of this design is that it forces the shooter to learn two different trigger pulls and accuracy often suffers on the first double action shot. Most accidental discharges with these sorts of pistols are the result of the shooter forgetting to decock the hammer.
Double Action/Single Action with De-Cocker Only – Ruger and SIG
This is a variant of the DA/SA which is used by Ruger, SIG and some others. It functions just like a DA/SA except the “safety” lever is not a safety. It only de-cocks the hammer, but the gun will still fire when the de-cocker is applied. I personally do not like this design since the de-cocker looks just like a safety lever but does not put the gun on safe.
Double Action Only – Glock, some Smith & Wessons, some Berettas, some Rugers, Kahr, Kel-Tec,.
This is the newest action design made popular by Glock. With these pistols every trigger pull is the same and they have no external safety or decocking levers. The hammers are not cocked by the cycling of the slide, except for the Glocks which are pre-cocked by the slide, and are not true double action. DAO pistols depend on the long double action trigger pull to prevent accidental discharges. In a sense these are autoloaders which fire like revolvers. Triggers vary from model to model. Some, like the Glocks, have very light triggers. Other DAO triggers can get quite heavy and long, and can be very upleasant to shoot. The advantage of this action is its simplicity and the fact that every trigger pull is the same.