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Old May 20, 2013, 08:33 AM   #1
mx03
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Single Action vs Double Action vs SA/DO

Can someone explain to me in "idiot" terms what thew difference is? I have done so much reading and I just DON'T get it. In a double action, don't you have to rack the slide back to chamber the round anyways just like in a single action?

Please, be easy.. I am a newbie and I feel dumb!
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Old May 20, 2013, 08:47 AM   #2
Iron Man
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Easy to explain, and I will do it for both revolvers and pistols. Also, there is a type of handgun that is also known as Double Action Only.

Revolver

Single Action -- the hammer must be manually cocked every time the pistol is fired.

Double action -- the hammer may be cocked prior to firing, but the pistol can be fired by pulling the trigger alone. Trigger pull is almost always much lighter if manually cocked first.

Double action only -- hammerless revolvers (e.g. Smith & Wesson J frames) are always in a state of "hammer down" and will have a heavier trigger pull to engage the firing mechanism.

Pistol (all pistols must have a round placed into battery before firing, which in most cases cocks the hammer).

Single Action -- After a round is in battery, if the hammer is dropped for any reason it must be recocked for the weapon to fire. The 1911 is a perfect example. The manufacturers recommended carry is cocked and "locked" (safety on).

Double Action -- After a round is in battery, the weapon may be fired as with a single action pistol, or the hammer (or striker) decocked. This is usually done with a lever (e.g. Sig Sauer, Beretta, Walther PP series) or button on the pistol (e.g. Walther P99). A block usually prevents accidental discharge in the case of a drop. These pistols may be fired with the hammer down or striker decocked, but the trigger pull will be heavier due to the extra effort of recocking the firing mechanism.

Double Action Only -- Like the aforementioned revolver a LDO pistol will always be in an uncocked state, regardless of whether or not a round is in battery. In some cases the trigger pull is still very light (e.g. Para Ordnance LDA) but many pistols will have a heavier trigger pull (e.g. Colt Double Eagle, Ruger LCP).
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Old May 20, 2013, 08:53 AM   #3
kraigwy
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Quote:
In a double action, don't you have to rack the slide back to chamber the round anyways just like in a single action?
Yes
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Old May 20, 2013, 09:05 AM   #4
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Think of it as the "HAMMER COCK" rather than the action of the slide. Both require initial chambering of the round by racking the slide. Once chambered, the SA gun requires cocking the hammer, either by hand or by the action of the slide. The dbl action gun allows the trigger to cock the hammer, just like a typical dbl action revolver.

So the SA pistol only has one ACTION of the hammer, it falls toward the round.

The DA pistol has a DOUBLE action or movement in order to fire. It first moves rearward (cocks) then the 2nd action is to fall forward, toward the round.

A dbl action ONLY gun goes through both actions every time it's fired. A DA/SA gun typically fires the first round DA, then subsequent rounds are fired SA, the action of the slide cocks the hammer. When you're finished firing a string, you release the hammer and allow it to return to the forward, lowered, DA state. You releaze that hammer either manually (thumb on hammer, pull trigger) like most 1911's, or use a de-cocker lever, like most Baretta M92's.


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Old May 20, 2013, 09:11 AM   #5
Aguila Blanca
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^^^ I think Kraig should have answered "Yes / No."

Single action/double action does not relate to chambering the next round. It relates to the hammer and trigger. I shoot 1911s, which are SA only. To chamber the FIRST round I have to rack the slide. After that, the movement of the slide ejects the empty case and loads (chambers) the next round. This is why pistols with slides and magazines are called "semi-automatic." The old term for them was "auto-loading." With this type of pistol, racking the slide also cocks the hammer, and pulling the trigger only drops the hammer (the "single" action).

If I take a SA/DA like an older S&W pistol, I still have to rack the slide to chamber the first round. But, if the hammer is down when the chamber is loaded, pulling the trigger first cocks the hammer, then releases the hammer (two actions, or "double action"). With the old S&Ws and other SA/DA pistols, firing the first shot leaves the hammer cocked, so all subsequent shots are SA.

In a double action only (DAO) pistol, you still have to rack the slide to chamber the first round. But ... racking the slide does not cock the hammer (or striker). Racking the slide loads the pistol, but it remains uncocked. Pulling the trigger first cocks the hammer (or striker), then releases the hammer (or striker) -- the two (double) actions. With this type of pistol, the movement of the slide does NOT cock the hammer or striker, so all subsequent shots are also double action.

Regardless of the action type, starting with an empty pistol you ALWAYS have to rack the slide to chamber the first round. The trigger cannot do this.
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Old May 20, 2013, 09:13 AM   #6
newfrontier45
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For the record, there's no reason to call a revolver DA/SA. It's redundant (like .38/.357) and unnecessary to differentiate from DAO (double action only). Nobody calls single action revolvers "SAO" either.
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Old May 20, 2013, 09:28 AM   #7
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Simple summary:

Single action: the trigger performs the single action of releasing the hammer or striker.

Double action: the trigger performs two actions, first cocking the hammer or striker, and then releasing it.

DA/SA: the first trigger pull is double action, cocking and releasing the hammer or striker, and then the subsequent pulls of the trigger are single action because the slide has cocked the hammer or striker.
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Old May 20, 2013, 10:02 AM   #8
MrBorland
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Quote:
Originally Posted by newfrontier45
For the record, there's no reason to call a revolver DA/SA. It's redundant (like .38/.357) and unnecessary to differentiate from DAO (double action only).
For the record, DA/SA and DAO aren't redundant (nor are .38/.357). Double Action Only revolvers have no hammer spur or SA sear, so the user doesn't have the option of cocking the hammer and shooting SA. To many, the difference matters quite a bit.
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Old May 20, 2013, 10:51 AM   #9
mx03
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Thanks everyone!

I don't know why but the way "Aguila Blanca" wrote it, i could actually picture everything perfectly... Im gonna type it as i took it and hopefully now i get it.

So, basically, every type of semi automatic needs to be chambered, but with a SA only, after every round is fired, the "hammer" is cocked by the slide and the trigger only releases the hammer to fire the round.

with SA/DA.. it works the same way as above, but if the hammer is down, the trigger cocks it and releases it rather than me having to cock the hammer manually or by the slide.

DA only, racking it only chambers the round and the trigger does everything.

How did I do for this test? :-)
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Old May 20, 2013, 11:13 AM   #10
newfrontier45
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For the record, DA/SA and DAO aren't redundant...
For the record, you misread my post.

"DA/SA" is redundant because it is a given that a DA revolver can be fired in SA mode. Just as ".38/.357" is redundant because it is a given that any .357 revolver can also shoot .38Spl's. I didn't say anything about DAO being redundant.
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Old May 20, 2013, 01:23 PM   #11
carguychris
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Quote:
DA only, racking it only chambers the round and the trigger does everything.
Basically yes... with a couple of caveats.

Many DAO pistols use a pre-set hammer or striker that is initially partially cocked by the slide. When the trigger is pulled, the hammer or striker is drawn back the rest of the way and released; the hammer or striker is then partially cocked again as the slide cycles. This system reduces the length and/or weight of the DAO trigger pull.

The reason this is significant is that many pre-set DAO pistols lack second-strike or repeat-strike capability- the ability to pull the trigger repeatedly and hit the same round multiple times if it does not fire on the first attempt. Pistols that lack this capability MUST be manually cleared in the event of a failure-to-fire, because the trigger does nothing once the hammer or striker is decocked. Common pistols that lack this capability include Glocks, the S&W M&P and Sigma series, Kel-Tecs, and the Ruger LCP and LC9.

Some pre-set DAO pistols do have second-strike capability, although a subsequent trigger stroke is usually longer and/or heavier than the initial DA pull; examples include HKs with the LEM trigger and SIGs with the DAK trigger.

Other DAO pistols do not have pre-set hammers or strikers, in which case the hammer or striker always starts from the same position, giving the pistol second-strike capability by default. Common examples include the Beretta 92D and 96D and the SIG P250. (In other words, the trigger works basically the same way as the trigger of a DA revolver, minus the ability to hand-cock the hammer for single-action fire.)

Other related notes...

Almost all traditional DA/SA hammer-fired pistols have second-strike capability.

A handful of DA/SA hammer-fired pistols feature a half-cock notch. Half-cock notches were originally intended as a safety feature on older SAO designs (although they were often dubiously effective as such); however, on a DA/SA pistol, they generally serve the same purpose as a pre-set hammer on a DAO pistol- i.e. reduction of the DA pull length and/or weight. DA/SA pistols with this feature include the CZ 75 and early versions of the Beretta 81-series (which includes the 84 through 87).
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Last edited by carguychris; May 20, 2013 at 01:29 PM. Reason: Added a little info...
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Old May 20, 2013, 01:47 PM   #12
newfrontier45
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IMHO, all this about "racking the slide" has nothing to do with the DA, SA, DAO explanation and probably only serves to cause confusion.

Also, DAO and striker-fired autos are different enough in design and function that they should really be considered separately. I would never refer to a striker-fired pistol like the Glock as DAO.
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Old May 20, 2013, 02:09 PM   #13
Aguila Blanca
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Quote:
Originally Posted by newfrontier45
"DA/SA" is redundant because it is a given that a DA revolver can be fired in SA mode.
What makes this a given? Not all DA revolvers can be fired in SA -- some are DAO, but they are still double action.

Quote:
Originally Posted by newfrontier45
IMHO, all this about "racking the slide" has nothing to do with the DA, SA, DAO explanation and probably only serves to cause confusion.
Considering that the question specifically asked about racking the slide, it would have been difficult to properly answer the question without discussing racking the slide.

Last edited by Aguila Blanca; May 20, 2013 at 02:16 PM.
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Old May 20, 2013, 02:22 PM   #14
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Re: post 12...

The OP told us he is a complete newbie.

Some of us have read about prosecutors who think a 1911 (SA) has to be manually cocked for each shot, because that is how they think Single Action works.

So, it is not a bad idea to mention that reciprocation of the slide cocks the hammer on SA and DA guns, because there are people out there who do not realize that, including some who should know better. (Edit: not referring here to the OP; referring to prosecutors of gun charges.)

It is also not a bad idea to point out that DAO pistols do not cock the hammer via slide movement.

Also, Smith and Wesson call the M&P line of striker fired pistols "DAO." IIRC, Kahr also consider their own line to be DAO.

Last edited by MLeake; May 20, 2013 at 04:33 PM.
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Old May 20, 2013, 02:23 PM   #15
mx03
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I think my question was actually answered well. I actually now get it.

The only questions i have now is:

If a semi automatic has an outer hammer. Can you cock it back yourself and then fire the gun or because the trigger does this for you, there is no need?

Also, someone mentioned about carrying a a double action with an outer hammer? Do semi automatic with an outer hammer have to have a safety so if in the "cocked" position, the trigger cant be pulled so easily?
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Old May 20, 2013, 02:31 PM   #16
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mx03, if the hammer fired pistol is DAO like my old SIG P239 SAS was, you could cock the hammer back, but it would fall forward without moving the firing pin, not stay cocked - which is the same thing it would do when the slide reciprocated (fall forward).

If the hammer fired pistol were single action, or conventional double action (sometimes called DA/SA), then the hammer would stay in the cocked position when you pulled it back.

SA pistols normally have at least one safety, for cocked and locked carry. Conventional DA pistols will typically have either a decocker, or a combined safety/decocker.

Some guns allow multiple function types. For example, the FN FNX can be carried cocked and locked, with the hammer back and the safety lever up. The FNX can then be shot in SA mode when the lever is lowered to horizontal. BUT, if the lever is pushed below horizontal, the FNX will decock and go into conventional DA mode.

Edit: Other relatively common variants on safety and cocking mechanisms would be those used by the CZ75 pre-B and B models, and the various HK P7 variants.

Edit: On safeties... some block trigger movement; some block hammer or striker movement; some block the firing pin.

Some prevent accidental firing due to premature placement of finger on trigger; some require the trigger be pulled; some protect against inertial movement of firing pin or striker due to an external impact on the weapon.

Last edited by MLeake; May 20, 2013 at 02:47 PM.
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Old May 20, 2013, 02:52 PM   #17
newfrontier45
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What makes this a given? Not all DA revolvers can be fired in SA -- some are DAO, but they are still double action.
Then obviously you would refer to them as "DAO" rather than a "DA", wouldn't you???
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Old May 20, 2013, 02:55 PM   #18
MLeake
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Not necessarily.

My Model 13 has a bobbed hammer, but it has the original sear. It could be cocked, if somebody wanted to start the hammer with a little bit of trigger pull, then hook the top front of the hammer.

It isn't DAO, but it certainly is easier (and safer) to shoot it as though it were.

Edit: For it to truly be DAO, I would have to swap out or modify the sear.
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Old May 20, 2013, 03:41 PM   #19
newfrontier45
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You guys are making this way more complicated than it needs to be. If it has a SA notch and can be cocked in that mode, regardless of whether or not the hammer has been bobbed, it's not a DAO.
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Old May 20, 2013, 04:20 PM   #20
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Please, be easy.. I am a newbie and I feel dumb!
Don't be afraid to ask. There is always someone here that is willing to help newbies learn. We were all newbies at one time in our lives. Anybody that makes fun of you is just trying to compensate for their own inadequacies or something. Welcome to TFL and the shooting world.
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Old May 20, 2013, 04:49 PM   #21
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"DA/SA" is redundant because it is a given that a DA revolver can be fired in SA mode.
Nope. Try to fire a S&W Centennial revolver in SA mode. You can have all day. Heck, you can have all week but you'll never, ever get that sucker to fire in SA mode.
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Old May 20, 2013, 06:36 PM   #22
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Quote:
Quote:
"DA/SA" is redundant because it is a given that a DA revolver can be fired in SA mode.
Nope. Try to fire a S&W Centennial revolver in SA mode. You can have all day. Heck, you can have all week but you'll never, ever get that sucker to fire in SA mode.
...Which is why the Centennial is considered a DAO revolver.
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Old May 20, 2013, 06:43 PM   #23
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"Double" action can have two meanings; first, that the trigger can both raise and drop the hammer, and B, that the gun can be fired in two ways, by either manually cocking the hammer and pulling the trigger, or by using the trigger to both cock and drop the hammer. The former is why "double action" is sometimes also called "trigger cocking".
Any semi-auto that requires racking the slide to reset the mechanism is not "double action", using either definition.
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Old May 20, 2013, 09:12 PM   #24
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...Which is why the Centennial is considered a DAO revolver.
Not by me, and not by anyone on earth before the development of the "wonder nines". The Centennial existed LONG before the creation of the appellation "DAO"
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Old May 20, 2013, 11:29 PM   #25
newfrontier45
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...Which is why the Centennial is considered a DAO revolver.
Exactly! Internal hammer, no single action notch in the hammer, that's pretty much the definition of DAO.

But you're right, before we started calling them DAO, we just called them double action only.
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