SA vs DA

[Phoebe]

In a gun with a hammer, SA vs DA seems obvious to me. (I think I understand it.)

But in a semi-automatic, I can't figure out what this translates to.

I've had my own gun apart (XD9) and looked at the inside of a Glock, so if any of this can be translated into either of those, it would be helpful.

I also don't fully understand hammers on semi-autos. (Why would you need or want one? How does it function on a semi?)

 

[rsxr22]

you have what is called a striker-fired gun. Glock, Springer, Smith and Wesson, etc. all incorporate these designs. They are neither SA or DA, but inbetween and normally closer to the DA side of the spectrum.

You get one consistent trigger pull with these guns. However, a SA/DA gun like some HK, Sig, Beretta, etc models have a exposed hammer. I personally started out only wanting striker-fired guns, but over the past year ive purchased 4 guns and only one (Glock 34) is striker-fired. An exposed hammer gives you restrike capability as well as a visual. Also SA/DA can be decocked into DA and for guns that dont have manual safeties, this acts as the safety. For example, my DA pull on my HK P2000 is 11 lbs and SA is 4.5. You have to train to shoot SA/DA if you are unfamiliar with them and really besides re-strike there is not a huge advantage to either and one is not better than the other.

The difference between a revolver SA/DA and a auto SA/DA, is: that unlike on a revolver, if you rack your semi and decock it, it will then be in DA. So your first shot will be DA but all of your follow up shots will be in SA because the slide will reset the hammer for you. On revolvers, obviously if you want to shoot in SA, you must manually depress the hammer

Hope that helps and i wasnt confusing,

 

[ATW525]

Most semi-autos have hammers. The main difference between a semi-auto hammer and revolver hammer is that the motion slide of the semi-auto can recock the hammer after each shot (some are designed not to, however, and are typically reffered to as double action only).

Striker fired guns work like hammer fired guns, only they use an internal striker in place of the hammer. The Springfield XD always shoots in single action, with the motion of the slide recocking the striker after each shot. The Glock shoots somewhere in between single and double action... the slide partially cocks the striker but the trigger still has to cock it the rest of the way before it will fire. Neither the glock or XD will fire if the trigger is pulled when the striker is completely decocked.

I've shot plenty of both hammer and striker fired guns and never noticed a huge difference in practical usage. The only thing I've ever noticed is that the double action hammer-fired gun has a minor safety advantage in reholstering since if you place your thumb on the hammer during the process you get tactile feedback if the trigger gets snagged.

 

[Dobe]

I also don't fully understand hammers on semi-autos. (Why would you need or want one? How does it function on a semi?)

My God, you are young. Oh, that's right, I'm old.

Single action autos are autos that requrire the shooter to cock the hammer or striker at least once. The recoil from the handgun cocks the handgun there after. An example in a hammer gun is the 1911, BHP, CZ 75B (single action model). An example in a striker gun is the P7. It is cocked by the squeeze cocker once, the P7 cocks the striker there afterwards. There is no way to simply pull the trigger on an uncocked single action handgun, and have it cock the hammer or striker.

A Double Action/Single Action commonly written as DA/SA is generally a hammer gun. This type of handgun can be fired or operated by cocking the hammer or simply pulling the trigger. There are many examples which range from CZ75B (DA/SA), HK USP, etc. Once the shooter fires the handgun by either cocking the hammer first or pulling the trigger, the hammer then is cocked by the recoil of the slide.

Now for the more recently developed striker handguns, termed safe-actions, the Glock comes to mind for most. There is no manual safety on a Glock, but rather a series of safety devices, which disable the gun's ability to fire unless the trigger is pulled. This is neither a doulble action, nor a single action handgun. The striker is partially under tension. The shooter, by pulling the trigger, completes the remaining tension needed while releasing the striker. You can look at this as double action light. Each sequential shot is the same.

Another catagory is the double action only handgun (DAO). This handgun has one and only one mode of firing. The shooter must pull the trigger, which cocks the hammer, each time he/she fires. This differs from a single action only in that the hammer must be cocked first, before the trigger is pulled, or the DA/SA handgun which can be fired SA or by pulling the trigger with the hammer cocked or by pulling the trigger with an uncocked hammer.

So why so many different varieties. Simple, its how we keep you young shooters in check. We know more than you. Just kidding.

The SA only handguns came from an era when liability and litigation were not the issues they are now. In fairness, SA only firearms were developed before much of the training techniques we have now.* With SA only, the shooter gets the same pull each time he/she fires. The pull is generally much lighter, and with less pull distance over a DA pull. Those that shoot DA/SA autos, generally do so, because it becomes less likely that that first round will be discharged due to sypathetic muscle contraction. In other words, it takes much more pressusre to pull off that first round, therefore it is unlikely you will discharge your handgun from being startled or surprised. The DA only handuns take it to another level. Every pull is long and requires about 12-15 lbs. of pressure. Some like this, because every shot is consistant. The safe-actions such as Glock are some where in between. Those handguns operate like a SA, but require a longer pull than most SA autos; the idea is to keep an unintentional shot from being fired.

Hope this wasn't too confusing.

* This can be as safe as other handguns, if the shooter is trained properly, and is willing to keep up the practice.

 

[sholling]

As rsxr22 said a striker fired pistol is usually somewhere in between. Racking the slide brings the striker to somewhere between 1/2 and 3/4 of fully cocked depending on the pistol. The long trigger 5-7lb pull then brings the striker to the fully cocked position before releasing it and firing the pistol. This is a good way to go and I have several pistols of this type.

A single action simply releases a fully cocked hammer. Because the trigger is doing one thing and only one thing (releasing the hammer) the trigger need only move a tiny fraction of a inch and can be lighter (4-6lbs) and more precise. That's a key part of the popularity of the 1911 and is partly why I own several.

Some like DA/SA but I can't stand them. With this politically correct scheme the first shot is a long double action pull where the trigger cocks the hammer like a revolver, then subsequent shots are single action. The problem is that the extreme change in the trigger pull between the first shot with its long and heavy (11-13lbs) trigger pull and the second shot with its short & light (5-6lbs) trigger pull way too often leads to the second going off before the shooter expects it and the shot going into the ceiling. Not good for the upstairs neighbor!

True double action only (DAO) is thankfully rare in a semiautomatic. This politically correct scheme is usually mandated by departments afraid of liability from poorly trained officers accidentally discharging their weapons. All shots require a long and very heavy trigger pull.

 

[Dobe]

The trend is going toward the striker guns. If nothing else, they are cheaper to make, requiring less parts.

 

[Mello2u]

One area of confusion in the use or misuse of the term double action. Logically, for there to be a double action there must be two ways the action works. Logically, if the action only works in one manner it can not be a double action.

Yet many manufactures use the phrase "double action only" [DAO] (an oxymoron - a figure of speech that combines two contradictory terms) to market a pistol which has an action which is partially cocked with a round chambered and then the shooter pulls the trigger to further add energy to either a striker or a hammer that is released during the trigger stroke and the pistol fires. Another variation of the DAO is one in which each pull of the trigger completely moves the hammer through its arc to the point of release.

kayla
In a gun with a hammer, SA vs DA seems obvious to me. (I think I understand it.)

But in a semi-automatic, I can't figure out what this translates to.

I've had my own gun apart (XD9) and looked at the inside of a Glock, so if any of this can be translated into either of those, it would be helpful.

I also don't fully understand hammers on semi-autos. (Why would you need or want one? How does it function on a semi?)

John Moses Browning is acknowledged as a firearms genius. He designed the 1911 and the Browning Hi-power about 100 years ago. The trigger action of well set-up 1911 is better than any other semi auto trigger action that I have tried. Getting a great trigger action is the main reason I can think of as to why one would want a hammer. It is not so much wanting a gun with a hammer as choosing the pistol design that you shoot best that happens to have a hammer as part of the design.

 

[Phoebe]

I don't know why I still find this confusing.

Maybe I'm a half step towards better understanding....but I doubt I've made any significant progress.

Maybe I need to take apart more guns.

 

[MLeake]

Double Action does not mean "two different modes"

It means the trigger performs two actions, cocking the hammer, and releasing the hammer.

A single action trigger is not capable of cocking the hammer; it only performs the single action of releasing the hammer.

There is nothing at all oxymoronic about a DAO. It's simply a double action (cock and release - two actions) trigger system that can't operate in SA mode. Sorry, Mello2U.

In response to Sholling, the only DAO auto I own is a P239 DAK, and it's 6lb pull is neither heavy nor long. It's very smooth, and it's very consistent, and I find it easer to shoot double-taps with it than I do with DA/SA setups. So, not all DAO actions are horrendous. Admittedly, some are, but there are some good designs out there, too. I have no trouble keeping a box of ammo in the scoring areas of the silhouette at 25yds with the P239; it's a great little gun.

The advantage to a hammer vs striker fired auto is in the event of a failure to fire, you can pull the trigger again on a hammer-fired pistol. You can't on a striker; the striker-fired pistol will require the shooter to manually actuate the slide to clear the round. With the DA, assuming it was just a hard primer issue, you can pull again, and it may fire. With an SA pistol, you'd have the option of cocking the hammer and pulling the trigger a second time, and it may fire. Of course, if it doesn't, you have to manually cycle the slide on the DA or SA auto, too.

An additional advantage to a hammer on DA or SA pistols is that you can lighten the force needed to rack the slide, by cocking the hammer and taking the mainspring tension out of the equation. With the striker-fired pistol, you have to contend with both recoil spring and mainspring force every time you rack the slide.

And, of course, with a DA/SA pistol you have the option of cocking the hammer to fire the first shot in SA mode, for reduced weight and length of pull.

With the exception of my Kahr, I have yet to shoot a striker-fired pistol that has as good a trigger feel as those on my hammer-fired pistols. So this for me is the primary reason I prefer a hammer on my autos. I'm all about the feel of a gun, whether it's the trigger, the balance, or the grip. I've rarely bought guns that didn't have a "just right" feel, and inevitably I've rid myself of those.

 

[MLeake]

Note to Kayla

SA autos are often carried in "cocked and locked" mode. This means a round in the chamber, the hammer back, and a safety (or multiple safeties) engaged. To fire the pistol, the safeties must be clicked or squeezed off, and then the trigger pulled. Trigger pulls are typically light (3.5-6lbs) and short.

Some of the more popular SA autos are the 1911 and its variants; the CZ75B (which can actually be carried in SA or DA mode); and the Browning Hi-Power. On the 1911 series, a grip safety must be squeezed (this happens when the pistol is gripped, it doesn't really require any additional step) and the thumb safety clicked down; on the CZ and BHP, there is no grip safety, just the thumb safety.

DA autos are usually carried with a round in the chamber, and the hammer down. Typically, the hammer is lowered by a decocker lever. DA autos may or may not have safeties. The Beretta decocker lever doubles as a safety, while the SIG decocker is only a decocker. The value of a safety on a DA auto is debatable; the primary argument in its favor is that it might momentarily confuse an aggressor who managed to take the weapon away. Personally, I prefer the decocker/no safety system on a DA pistol.

DA autos can be in either DA/SA or DAO modes, as noted in a couple of the above posts. In the DA/SA pistols, the cycling of the slide during the recoil phase of each shot cocks the hammer, which stays back so that subsequent shots are in SA mode (trigger doesn't need to cock the hammer, it's already back); the trigger only has to release the hammer - if the shooter wants to cease shooting, the decocker can be used to lower the hammer again. In the DAO pistols, the hammer goes back when the slide moves rearward, but it doesn't stay back; instead, it rides forward with the slide to a partial or half-cock position. The trigger then has to fully cock and release the hammer (two actions again) for every shot.

Popular DA/SA 9mm autos include the Beretta 92, SIG P-Series, S&W pistols, and quite a few others.

I'm not sure there are any truly popular DAO pistols in terms of sales volume, but the P239 and P229 DAK pistols have their adherents. Beretta 92s can be had in DAO mode, typically due to large orders by police departments.

Some pistols, like the CZ75 Omega and the HK USP, can have their controls switched around so that they can be used with a safety for SA/cocked and locked carry, or a decocker for DA/SA carry.

Hope that helped.

M

PS: with regard to safeties, I only mentioned those that are actively manipulated by the shooter. Some weapons have firing pin blocks, inertia safeties, and other devices that work automatically when the trigger is pulled, but since there are no actual steps the shooter must take for those, I'm not going into any more detail on them.

 

[Dobe]

Let's look at this with a revolver in mind. Some of these terms originated from revolvers anyway.

Take a standard double action police type revolver that you may have seen. You can cock the hammer with your thumb and then pull the trigger (SA or single action), or you can simply pull the trigger without cocking the hammer first (DA or double action). The former takes very little trigger pressure, and little pull length. The later takes much more pressue and pull length. The term comes from the fact that you can fire the revolver both ways, thus a double action revolver. The actual DA part (pulling the trigger without cocking the hammer) is just a way to distinguish that mode from the SA mode.

The DAO (double action only) is the ability to pull the trigger witout cocking the hammer first, but with no option of cocking the hammer. Each time you fire, the hammer does not reset, but follows the slide to an uncocked position. Each tiime you fire, you must recock the hammer by pulling the trigger. Double action in this context is just a hold-over of expressions. The mode has been and probably will forever be called DA, because of the history of the DA revolver. Therefore, if the gun can be fired by pulling the trigger, and that pull also completely cocks the hammer, it is a DA handgun. A DAO will not allow a SA mode.

The DA/SA allows for both initial modes of operation, but the hammer remains cocked after each firing, which places all shots but the inital shot in SA mode. You fire initial shot in either DA or SA, the hammer remains back for follow-up shots in SA mode.

 

[MLeake]

Again...

"Double Action" means the trigger performs two distinct actions: it cocks the hammer, and it releases the hammer.

It does NOT mean that the trigger system necessarily has two modes. It might (DA/SA), but it might not (DAO). Either way, it's "double action."

 

[Dobe]

DA is a holdover from revolvers. A double action revolver is not a DA/SA revolver. It is a double action revolver. The double did not come to mean the DA does two actions.

 

[Dobe]

http://www.youtube.com/watch?v=mM9YWPywIXI&feature=fvw Kayla, don't pay any attention the the method he is using to hold this hand gun or his trigger finger placement. Look at the fact he is pulling the hammer back by using the trigger. This is the a DA pull. If the trigger had been cocked first, it would have been an SA mode. If the handgun would not allow the shooter to cock the handgun first, it would be a DAO.

This is a very poor video, but one I could quickly find.

 

[MLeake]

From Wikipedia:
Double-action (DA)
Invented by Robert Adams, a double-action trigger performs two functions when pulling the trigger, first cocking the hammer then releasing it to discharge the firearm. When this term is applied to revolvers, the trigger also rotates the cylinder. Though this is technically a third action, it is correct to refer to the mechanism as double-action. Most pistols and revolvers with a double-action trigger mechanism retain the single action functionality: See the Double action/Single action (DA/SA) description below.[1]

From About.com:
Definition: Double action (DA) refers to any gun which can be cocked and fired by a single pull of the trigger. This term most often refers to handguns (pistols and revolvers), but properly applies to any gun that works the same way.

From dictionary.com:
dou⋅ble-ac⋅tion  [duhb-uhl-ak-shuhn] Show IPA
–adjective
(of a firearm) requiring only one pull of the trigger to cock and fire it.
Origin:
1850–55

From britannica.com
development of pistols ( in small arm (military technology): Revolvers )
...the Smith & Wesson patent expired in 1872, a host of new revolver designs appeared in the United States and Europe. The most important innovations were quick ejection of spent cartridges and double-action cocking. By linking the trigger to the hammer-cocking and cylinder-revolving mechanisms, double action permitted a pistol to be..

 

[Dobe]

You have confirmed what I have said. I know you went to some effort in looking this up. The DA/SA nomenclature derived from the SA revolver to the DA revolver to autos. While a DA auto will certainly and must certaily handle two functions, that is not from were the name is derived. A DA revolver was a DA revolver, because of the two distinct modes of operation. The term DAO was used with revolvers before it was use with autos. It was called DAO, because the remaining mode (the DA mode) was the only mode left.

Now, back to Kayla's problem.

 

[rsxr22]

Kayla

my best advice if you are still confused is to visit a local gun shop. A good salesman will be able to demonstrate the things that i and others have explained.

The real advantage though of an exposed hammer is the re-strike capability. That is its main advantage. For examle, on a revolver, if you pull the trigger and the gun does not go bang because of a bad round or maybe a light strike, the cyclinder will turn and give you a fresh round. On a DA/SA semi-auto, if you pull the trigger and the gun doesnt go bang because of the same issues, you can pull the trigger again and the pull might fire. If it doesnt you must rack the slide to eject the bad round. On a striker-fired gun like your xd-9, if your gun fails to fire, you must immediately rack the slide to eject the bad round and chamber a new one because on striker fired guns there is no restrike capability.

 

[Dobe]

http://www.youtube.com/watch?v=KtVluGslhMs This video sounds like it's being narrated by Mr. Rogers, but he gets the point across.

 

[MLeake]

Dobe...

... none of my lookups including the one from 1855, mention two different modes as part of the definition of DA. It's all about cocking and firing.

DA/SA is a derivative term for semi-autos, but the original definition of DA for revolvers had NOTHING to do with two modes of operation, just two distinct actions by the trigger.

Find a source that defines double action as having to do with two modes. I couldn't.

 

[Dobe]

Give me some time. I'll get back with you tomorrow.

Update: The definitions you gave are certainly accurate, but only define 'How' it works. It will take some time, but if I can find it, I will.