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Old February 4, 2006, 06:17 PM   #1
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DA and SA

What is the difference between double action and single action? Pros and cons?
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Old February 4, 2006, 06:40 PM   #2
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Well, I will try and answer the part of the question to what seems to be a defintion question.

Double action is defined as the relationship between the trigger and the hammer; in that the trigger does two (double) actions. In the double action, the trigger draws back the hammer as well as the second action of "triggering" the hammer to move forward striking the firing pin setting off the cartridge.

Single action requires the handler to manually draw the hammer back with one's hand, firstly. Only then may the trigger may be pulled, releasing the hammer to move forward striking the firing pin and then thusly setting off the cartridge, performing only a single action.

I will leave advantages/disadvatages to others that are more knowledgeable than I.

I hope this is both an accurate as well as informative reply.
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Old February 4, 2006, 08:25 PM   #3
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There are three basic types of semi-auto trigger systems; Double action only (dao), single action only (sao) and double action/single action (da/sa).

With a double action only system the trigger both cocks and releases the hammer/striker with every trigger pull. Examples: Glock, Kahr, dao law enforcement versions of popular da/sa pistols. Pros: as opposed to da/sa a dao system gives a consistent trigger pull for every shot. A dao trigger is generally considered to be safer than a sao trigger and requires no manual safety for safe carry, and a dao does not have to be decocked like a da/sa to be carried safely. Cons: a dao gun will have a much heavier trigger than sao or da/sa guns, this can adversely affect accuracy and speed of shooting.

With a single action only system the hammer/striker is cocked by the movement of the slide for every shot, including the first. Examples: 1911, Browning Hi-power, most rimfire semi-auto and competition pistols. Pros: A sao trigger has a consistent trigger pull from first to last shot, unlike a da/sa, a sao trigger will typically be much more crisp and have less takeup than a da/sa single action pull, and will be far lighter with a fraction of the travel of a dao, generally a sao gun is easier to shoot accurately and quickly than either dao or da/sa guns. Cons: Sao guns require a manual safety to be carried safely. To safely carry a sao gun you must be familiar with the functions and handling of the gun. If a round fails to fire you cannot simply pull the trigger to try again, the hammer must be manually cocked or the slide racked (though some dao systems such as Glock's or Kahr's suffer the same setback)

With double action/single action systems the first shot functions in double action, while subsequent shots function as single action. Examples: H&K usp, Sig Sauer, Beretta 92. Pros: Da/sa combines the safety aspects of double action and the accuracy and speed aspects of single action. Almost all da/sa systems will allow you to simply pull the trigger again to try to fire a round that failed to ignite. Cons: a da/sa typically will have a sloppier "two stage" single action trigger pull than a sao, although the trigger pull will typically be quite light and capable of accuracy and speed. Da/sa triggers have to be decocked after chambering a round to carry safely, some decockers are safer than others and decocking a gun by pulling the trigger and easing the hammer down is incredibly unsafe (don't do this with sao pistols either! 1911s were designed to be carried with the hammer cocked and manual safety engaged). Da/sa results in an inconsistent trigger pull as the first shot will have a heavy, long da pull and subsequent shots will have a light sa pull.

I hope that helps. In case you were curious, I tend to prefer da/sa triggers myself although my primary concealed carry piece is a dao Kahr and I am quite happy with it. If I were shooting a competition where accuracy was the only consideration I would go with a sao system.
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