Need Explanation of DAO, SA, and DA/SA

Need Explanation of DAO, SA, and DA/SA

This is a discussion on Need Explanation of DAO, SA, and DA/SA within the Defensive Carry Guns forums, part of the Defensive Carry Discussions category; If there is an existing thread on this, please let me know and you can then ignore this post. I will search the thread. But, ...

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Thread: Need Explanation of DAO, SA, and DA/SA

  1. #1
    Distinguished Member Array Ron's Avatar
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    Need Explanation of DAO, SA, and DA/SA

    If there is an existing thread on this, please let me know and you can then ignore this post. I will search the thread. But, here are my questions. I now use as my carry gun a S&W 642, which I like a lot. It carries nicely in a pocket holster, and I am quite accurate with it at the range, but find it a bear to shoot because of the recoil(yes, I am probably recoil sensitive), and so have found that I am not practicing with it as much as I would like, and think that I should. So, as I posted on another thread, I am presently exploring buying a compact semi-automatic in 9mm. In researching the various compacts available, I have noticed that they come in different trigger formats. I think that I understand what DAO is. My understanding is that the hammer is not cocked until you pull the trigger. Each time you pull the trigger, it cocks the hammer and then releases it so that, although you have a round in the chamber, assuming you have racked the slide, you are never carrying a fully cocked gun. I think that I also understand what SA is. My understanding is that the hammer is always cocked, so that you are always carrying a fully cocked gun, a concept that makes me a bit unsettled if you have racked the slide and have a round in the chamber, notwithstanding that I also understand that they will almost always have a manuel safety. What I dont fully understand is the DA/SA configeration, such as on the Taurus PT111 and some other pistols. Am I correct that when you first rack the slide it both cocks the hammer and puts a round in the chamber, but the first pull is lighter, as in SA, and then each subsequent pull of the trigger cocks the hammer, but the trigger pull is longer, as in DO, so that you are always carrying a fully cocked hammer, but, at least in the PT111, with a manuel safety?

    If my assumptions about these differences are incorrect, can someone please correct and enlighten me.

    I am also unclear about what trigger format is on the XD SC9mm, M&P compact9mm, and Walther compact 9mm. Again, I will very much appreciate help with this.

    Lastly, how much of a real concern is it to be carrying a gun with a round in the chamber and a cocked hammer?

    PS: Sorry about the lengthy post.

    Ron
    Last edited by Ron; January 1st, 2007 at 01:37 PM.


  2. #2
    Member Array Desk Jockey's Avatar
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    I'm sure someone will explain it better in few minutes. I had the same questions when I started looking at semi-autos.

    DAO - You're right. There is no option to cock the hammer manually, each trigger pull cocks the hammer and fires the gun. Several (most, all?) DAO autos have no safety other than the long trigger pull and the safety between your ears.

    SA - Pulling the trigger does not cock the hammer. For the first shot, the hammer must be cocked manually. After that, the hammer is cocked by the slide. There is always (?) a safety or decocker on these guns. With a safety, you can carry "cocked and locked". Or, on some SA's, you can carry with the hammer in a half-cock or hammer-down position. Perhaps safer, but requires that you cock the hammer manually before you can fire.

    SA/DA - Pulling the trigger with the hammer down will cock the hammer and fire the gun (assuming no safety or decocker is engaged). The slide cocks the hammer for subsequent shots. Or you can cock the hammer manually if you want to. Usually, you would carry with the hammer down. Then the first shot is double-action and everything after that is single action (hammer cocked by slide).

    The decocker is a lever that lowers the hammer safely without firing the weapon. On some pistols, it also disengages the trigger when it is in the 'decocked' position. Without a decocker, you must lower the hammer manually.

  3. #3
    VIP Member Array Bud White's Avatar
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    Quote Originally Posted by Desk Jockey View Post
    I'm sure someone will explain it better in few minutes. I had the same questions when I started looking at semi-autos.

    DAO - You're right. There is no option to cock the hammer manually, each trigger pull cocks the hammer and fires the gun. Several (many?) DAO autos have no safety other than the long trigger pull and the safety between your ears.

    SA - Pulling the trigger does not cock the hammer. For the first shot, the hammer must be cocked manually. After that, the hammer is cocked by the slide. There is always (?) a safety or decocker on these guns. With a safety, you can carry "cocked and locked".

    SA/DA - Pulling the trigger with the hammer down will cock the hammer and fire the gun (assuming no safety or decocker is engaged). The slide cocks the hammer for subsequent shots. Or you can cock the hammer manually if you want to.

    The decocker is a lever that lowers the hammer safely without firing the weapon. On some pistols, it also disengages the trigger when it is in the 'decocked' position. Without a decocker, you must lower the hammer manually.
    ya pretty much hit it on the head

  4. #4
    Member Array Hobbes's Avatar
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    Your correct about it all except the DA/SA. You load the weapon, and when the slide goes forward, the hammer will be cocked. Push the decocker and that's how you carry it. (there are a few exceptions to this like the HK USP that can be carried decocked or cocked and locked)
    The first shot is then DA and subsequent shots are SA.

    It is perfectly safe to carry in SA with the manual safety engaged (this is called cocked& locked and is the ONLY safe way to carry SA only guns such as the 1911)

  5. #5
    Distinguished Member Array Fitch's Avatar
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    DA/SA with decocker is great for CCW.

    Quote Originally Posted by Desk Jockey View Post
    I'm sure someone will explain it better in few minutes. I had the same questions when I started looking at semi-autos.

    DAO - You're right. There is no option to cock the hammer manually, each trigger pull cocks the hammer and fires the gun. Several (most, all?) DAO autos have no safety other than the long trigger pull and the safety between your ears.

    SA - Pulling the trigger does not cock the hammer. For the first shot, the hammer must be cocked manually. After that, the hammer is cocked by the slide. There is always (?) a safety or decocker on these guns. With a safety, you can carry "cocked and locked". Or, on some SA's, you can carry with the hammer in a half-cock or hammer-down position. Perhaps safer, but requires that you cock the hammer manually before you can fire.

    SA/DA - Pulling the trigger with the hammer down will cock the hammer and fire the gun (assuming no safety or decocker is engaged). The slide cocks the hammer for subsequent shots. Or you can cock the hammer manually if you want to. Usually, you would carry with the hammer down. Then the first shot is double-action and everything after that is single action (hammer cocked by slide).

    The decocker is a lever that lowers the hammer safely without firing the weapon. On some pistols, it also disengages the trigger when it is in the 'decocked' position. Without a decocker, you must lower the hammer manually.

    That's pretty much it. Your discussion of the decocker is pretty good too but from personal experience I'll add this:

    On my PPK/S, which is a DA/SA pistol with a decocking/safe lever, the decocker with the "safe" position is a huge feature for CCW purposes. With the decocker in the "safe" position, the gun can be loaded, including racking a round into the chamber, unloaded including removing the round from the chamber, with no chance that it will accidentaly discharge. With the decocker in the safe position, if the gun is dropped it will not discharge because it can't. It gives me peace of mind. My biggest worry when considering carrying was how to be sure there was the lowest possible chance of accidental discharge.

    With the DA trigger pull being heavy, there is very little chance of accidental discharge by pulling the trigger. The SA trigger pull is glass-break crisp permitting very accurate shooting for such a little pistol.

    I believe some other DA/SA pistols also have these features, but since I don't have personal experience with them I can't say for sure.

    Fitch

  6. #6
    VIP Member Array ccw9mm's Avatar
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    There is a write-up on HowStuffWorks.com, describing machine guns. But part of the article covers the mechanicals, with interactive graphics, so that you can actually see what's happening as a gun is feeding, firing, ejecting.

    There is also a pretty good graphic (flash?) floating around that shows a Heckler-Koch USP pistol going through its firing sequence. It's a classic double-action pistol, showing the firing in slow-motion.

    Basically: SA = the single action of dropping the hammer; DA = the double action of both cocking the hammer and dropping the hammer; DA/SA = DA on the first pull, but SA thereafter. Machine guns, of course, fire multiple rounds per trigger pull, automatically feeding/ejecting the bullets as they're fired.
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  7. #7
    Member Array Hobbes's Avatar
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    Yes, other guns do have that feature (Beretta 92 comes to mind). See, I like my PPK because it can also be safely carried with the safety off. Newer PPKs also have a firing pin block, so even with the safety off it won't discharge even if you drop it.

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    VIP Member Array Blackeagle's Avatar
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    Quote Originally Posted by Fitch View Post
    I believe some other DA/SA pistols also have these features, but since I don't have personal experience with them I can't say for sure.
    There are basically three types of decockers/safties for DA/SA pistols.

    Decocker only: This is a spring loaded lever which functions only as a decocker. When you let go of it it springs back to it's original position. The only safety is the long trigger pull (and the one between your ears, of course). This system is found on SIG's DA/SA pistols.

    Two position Decocker/Safety: The lever has a fire position and a safety/decock position. Activating it decocks the hammer and activates a safety. This sort of gun can be carried two ways: with the decocker/safety off (relying on the long trigger pull for safety) or with the decocker/safety on (meaning you'd have to remove the safety before firing). This system is found on the Beretta 92/M9, and many S&W autoloaders.

    Three position Decocker/Safety: This system allows you to decock and activate the safety separately, rather than linking the two actions as the two position system does. Pushing the lever in one direction acts as a springloaded decocker, similar to the decocker only. Pushing the lever in the other direction acts as a manual safety. This gun can be carried three ways: decocked with the safety off (relying on the long trigger pull for safety), cocked with the safety on (cocked and locked like a 1911), or decocked with the safety on (the suspenders and belt approach). This is probably the least common of the three systems, found on some variants of the HK USP series and a few other pistols.

  9. #9
    Member Array ispcapt's Avatar
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    Here ya go. The dictionary of firearm related definitions:
    https://www.midwayusa.com/guntecdictionary.exe/browse

  10. #10
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    ccw9mm & ispcapt...

    Thanks for some excellent reference materials that have been added to my favorites...



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  11. #11
    Distinguished Member Array Ron's Avatar
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    Quote Originally Posted by Desk Jockey View Post
    I'm sure someone will explain it better in few minutes. I had the same questions when I started looking at semi-autos.

    DAO - You're right. There is no option to cock the hammer manually, each trigger pull cocks the hammer and fires the gun. Several (most, all?) DAO autos have no safety other than the long trigger pull and the safety between your ears.

    SA - Pulling the trigger does not cock the hammer. For the first shot, the hammer must be cocked manually. After that, the hammer is cocked by the slide. There is always (?) a safety or decocker on these guns. With a safety, you can carry "cocked and locked". Or, on some SA's, you can carry with the hammer in a half-cock or hammer-down position. Perhaps safer, but requires that you cock the hammer manually before you can fire.

    SA/DA - Pulling the trigger with the hammer down will cock the hammer and fire the gun (assuming no safety or decocker is engaged). The slide cocks the hammer for subsequent shots. Or you can cock the hammer manually if you want to. Usually, you would carry with the hammer down. Then the first shot is double-action and everything after that is single action (hammer cocked by slide).

    The decocker is a lever that lowers the hammer safely without firing the weapon. On some pistols, it also disengages the trigger when it is in the 'decocked' position. Without a decocker, you must lower the hammer manually.
    I am still a bit confused on SA/DA. Pardon my ignorance about semi-automatics, but are you able to actually raise or lower the hammer manually on the 9mm XD, M&P or Walther compacts? I did not think so. And is there a "decocker" lever on those guns? Again, I did not think that there was one. Or, very likely don't know what a "decocker" lever is. What happens when I load a full magazine and then rack the slide. I thought that it automatically cocks the hammer, and you have no choice but to carry in the cocked position. unless there is a decocking lever. Am I wrong on this?

    And, can anyone tell me what the trigger configeration is on those guns?

    Thanks.

    Ron

  12. #12
    Member Array Hobbes's Avatar
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    Well, at least a couple of the guns you mentioned are not DA/SA guns. They have something completely different, basically a pre-cocked striker. The striker (no hammer on most of these guns) is sort of half cocked which gives some benefits of both SA and DA- a somewhat decent trigger pull (sometimes ;) ) but longer than a SA.
    Glock, XD, HK LEM, Sig DAK, Walther QA and M&P all fall into this pre-cocked striker category. The walther does have a de-cocker, but ONLY for disassembly purposes, I do not believe the rest have a decocker.

    On a true DA/SA gun, the de-cocker only serves to lower the hammer safely on a loaded chamber. Imagine thumbing the hammer down on a cowboy gun- this is what a de-cocker does, except it takes out the possibility of slipping and having a negligent discharge. And as already stated, some decockers also serve as a safety, again the Beretta 92 comes to mind. Guns such as the Walther AS (DA/SA) has just a regular decocker only.

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    VIP Member Array Blackeagle's Avatar
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    Quote Originally Posted by Ron View Post
    Pardon my ignorance about semi-automatics, but are you able to actually raise or lower the hammer manually on the 9mm XD, M&P or Walther compacts?
    The XD and M&P are both striker fired, so there is no hammer.

    You can basically divide DA pistols into two categories: those where all the energy to compress the hammer spring comes from pulling the trigger, and those where some of the energy comes from the cycling of the slide. On early DAO autopistols and the DA portion of most DA/SA types the hammer (or striker) spring is completely at rest when the hammer is down. Pulling the trigger moves the hammer/striker back and compresses the string. This can lead to a very long, heavy trigger pull, just like a DA revolver (SIG's early DAO pistols were sometimes referred to as 'flat revolvers').

    Starting with Glock, many manufacturers have come out with DAO pistols using the second system. The hammer/striker spring is partially compressed by the action of the slide (on weapons with exposed hammers, the hammer usually remains all the way forward, so it looks just like a true double action). Pulling the trigger moves the hammer back and compresses the spring the rest of the way. This allows a lighter, more controllable trigger. It's still longer and heavier than a SA trigger (primarily for safety purposes). The Glock, Springfield XD, SW M&P, SIGs with the DAK trigger and HKs with the LEM trigger all work this way.
    Last edited by Blackeagle; January 1st, 2007 at 05:27 PM.

  14. #14
    Distinguished Member Array Ron's Avatar
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    Thanks everyone. This is now beginning to make some sense to me.

    Blackeagle, do you know if the Taurus PT111 works the same way as the Glock and others you mentioned?

    Ron

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    VIP Member Array ccw9mm's Avatar
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    Ron, the thing to do might be to hang out at the range for a couple hours, renting a few different kinds of pistols. Showing genuine interest, you can get most anyone to take you through the paces.

    Remember: SA means that pulling the trigger does one thing only (dropping the hammer); whereas DA or DAO means that pulling the trigger does two things (cocks the hammer, then drops the hammer); and DA/SA is a hybrid, where the first shot is DA but all remaining shots are SA.

    SA revolver examples might include the original Colt revolvers from the late 1800's, where the hammer had to be cocked separately in order to bring the next bullet into play, then the trigger fired the gun.

    SA pistol examples include the venerable 1911 style pistol. A single pull of the trigger only does one thing: drops the hammer. Hence, you must already have either (a) cycled the slide to cock the hammer, or (b) manually cocked the hammer. This SA nature is why, generally speaking, folks carry the 1911 pistol "cocked and locked," so that the hammer has already been cocked, the safety is on, and it's ready to fire the moment the safety's off and the trigger's pulled.

    DA examples include most all modern revolvers, where simply pulling the trigger does both the (1) cycling of the next round and (b) firing of the bullet. Of course, with an exposed hammer, you can also treat it as if it were a SA revolver and do it in two steps, by first cocking the hammer and then pulling the trigger. The Kahr line of pistols is a good example of a DA or DAO style.

    Semi-auto DA pistols are also plentiful, but then DA/SA are as well. Basically, they both work the same on the first shot, where a single pull of the trigger does two things ... cocks the hammer and then fires the bullet. DA/SA varies the second and subsequent shots slightly such that the next pull of the trigger simply fires the bullet, as the cycling of the gun leaves the hammer already cocked back. On a pistol, DA can also be called DAO, where all rounds fired have the same cycling and pull as the first pull.

    Of course, as Blackeagle and others mention, there are variations on what "cocks" the gun, whether there's a hammer, whether the slide cocks the hammer again, and so on.

    Clear as mud?

    IMO, once you fire a couple magazines' worth through each type, you'll understand it completely. Simple, once you've seen each work. Any excuse is a good excuse to spend more time at the range. :)
    Your best weapon is your brain. Don't leave home without it.
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