Why are they called Double Action?


PDA






Ringer
September 19, 2004, 09:18 AM
OK, maybe this is a dumb question but why are guns like Para LDAs and Kahrs called double action? They seem closer to single action with a long travel since they are "somewhat" pre-cocked by the action of the slide traveling rearward. To me double action means I can pull the trigger (repeatedly) and have the firing pin/striker activated by nothing other than the trigger pull.

:confused:

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stans
September 19, 2004, 09:50 AM
Any handgun in which the hammer starts in the full down position and a pull of the trigger both pushes the hammer to the rear and releases it to fire the weapon is called double action. Many double action pistols are double action for the first shot, then single action for each additional shot. Others, such as the Para LDA, are double action only, there is no capability for the hammer to be cocked in a single action fashion.

Mulliga
September 19, 2004, 10:34 AM
Because the BATFE doesn't have a better classification for it? :)

Seriously, though, I agree. The Glock/Kahr/etc.-style pre-cocked striker fire system needs another term.

shu
September 19, 2004, 11:23 AM
they are called double action because two separare single actions (cocking hammer, releasing hammer) are accomplished by a single action of pulling the trigger.

single actions, contrariwise, are so called because firing the pistol is *not* accomplished by the single act of pulling the trigger but rather requires double actions of first cocking and then releasing the hammer.

dao, or double action only, are so named because the single action of firing the pistol can only be accomplished by the single action of pulling the trigger; that is, cocking and releasing the hammer cannot be done separately.

hope that clears it up for you. if it does not, just remember that sass, the single action shooters society, is a group of 19th century revolver afficionados (or rather a group of afficionados of 19th century revolvers).

Blueduck
September 19, 2004, 05:02 PM
OK, maybe this is a dumb question...

Certainly not a dumb question because what people including manufacturers are calling these type of guns IS hisorically incorrect, but DAO has become the term of common usage so it's too late to go back and fix it now :(

I think we also need a term to separate true "Double Action Only" (sic I know) systems like the Beretta 92D's from "assisted double action only" guns like the Sig DAK and HK LEM. But then you really also need a classification within those guns to determine which ones have an emergency second strike feature (VERY heavy DA trigger pull for second attempt from totally uncocked position, think the LEM is like this?), compared to guns like Glock which have no such feature at all.:banghead:

jc2
September 19, 2004, 07:42 PM
Historically, DA is when pulling the trigger performs a DOUBLE action: 1) Cocking the handgun (compressing the mainspring or striker spring), and 2) firing the handgun (releasing the hammer or striker). A second strike capability, while common in DA/DAO handguns, has never been part of the definition.

JohnKSa
September 20, 2004, 12:05 AM
In a single action, the trigger releases a cocked hammer or striker. It performs only that one function--a SINGLE ACTION.

In a double action (sometimes called a trigger cocking action or trigger cocker) a single pull of the trigger will both cock the firearm and drop the hammer. The trigger performs TWO functions--cocking and firing--or a DOUBLE ACTION.

In most cases, a double action gun can also function identically to a single action gun by manually cocking the hammer. This type of gun is sometimes called a DA/SA when it is an automatic, but it is understood that DA when applied to a revolver does not rule out the capability to cock the hammer and fire SA.

Then, someone got the bright idea that it might be beneficial to have a double-action gun that DIDN'T have the SA capability. The trigger cocks and fires the gun with a single pull, but the hammer can't be cocked for SA functionality. These guns are called DAO, and it was when they became common that you began to see the DA/SA designation on DA semi-autos to clarify the difference.

With revolvers, it's fairly simple. You either cock the hammer or pull the trigger, or both. For the most part, it's your fingers doing all the work. On an auto it gets a bit more complicated. The slide can also do work.

In an SA auto, the hammer must be manually cocked for the first shot (either directly or by manually operating the slide), but after the first shot, the slide action cocks the hammer automatically.

In a DA (DA/SA) auto, the hammer can be cocked manually as with the SA, but it can also be fired from the hammer down position by merely pulling the trigger.

NOW, what about DAO. Well, the slide doesn't cock the hammer, and the hammer can't be manually cocked--the only way to fire the gun is by pulling the trigger.

But the auto can be made a bit more complicated. Suppose the slide action PARTIALLY cocks the action. Now the trigger acts like a DA trigger in some ways--it must finish cocking the action and then release the hammer. But it functions like an SA in another way. Without slide action to perform the partial cocking, it can't do anything at all. That's the Glock action in a nutshell. The trigger does SOME cocking and also releases the striker. BUT, it can't do ANYTHING unless the slide has pre-tensioned the striker already.

Glock called it a SAFE-Action since it clearly doesn't function like a typical DAO action as you pointed out. However, BATF classified it as DAO for their purposes. If you handed the gun to someone and asked them to classify it based ONLY on the way the trigger functions (no fair peeking at the internals), they would have to classify it as SA--the trigger only functions after the slide has been manually operated--just like an SA with a concealed hammer would work. For example, the Springfield XD is actually a true SA (the slide fully cocks the striker) even though from the outside it's impossible to tell that it's any different from the Glock.

For some more twists, you can also have the slide reset the trigger mechanism WITHOUT performing any cocking function at all. In that case you would have a true DAO without a second strike feature. OR, you can also design a gun to make the slide tension a spring while the hammer appears to stay uncocked. The trigger then cocks the hammer, but without having to tension a spring--that gives a very light pull--might feel like a long SA pull-- with what appears from the outside to be a DAO.

For some reason, in spite of the obvious differences between a typical DAO and the Glock action, there are those (BATF for one ;) ) who insist on calling it a DAO. I suppose there's no harm in it as long as one understands what's going on inside the pistol.

jc2
September 20, 2004, 07:30 AM
This type of gun is sometimes called a DA/SA when it is an automatic, but it is understood that DA when applied to a revolver does not rule out the capability to cock the hammer and fire SA.
The above statement may be a little confusing for some. There are revolvers that do NOT have the capability "to cock the hammer and fire SA" as stated. Ruger, S&W and Taurus make models that are DAO--some with enclosed hammers and some with hammers in which the single action notch has been removed. Also, it is not unusual to find former LE revolver modified so they cannot fire SA.

The Glock is actually a true DAO handgun. While the action of the slide sets the striker (and must do so in order for the weapon to fire), the action of the slide does not compress the striker spring enough to fire weapon--it merely holds the striker just behind the breech face.. In other words, the trigger still must compress the striker spring before there is enough energy stored in it to ignite the primer. When a Glock sets the striker, it does so primarily as a safety measure--if the striker is not set, it will protrude out of the breech face and cause a slam-fire (full-auto function). The Glock action may feel like a SA, but it is done in a combination of the connector and trigger return spring--not by compressing the striker spring. Pulling the trigger still compresses the striker spring (function one) and releases the striker (function two).

Island Beretta
September 20, 2004, 10:42 AM
Second strike capability is actually inherent in the definition of a DAO since the strike is fully dependent only on the trigger pull. Other systems requires something else e.g. the slide or hand or belt to provide that cocking function (full or partially) with the trigger only being used to complete ala Glock that cocking function and/or then trip the sear.

The Glock cannot be a DAO in the traditional definition of a DAO since the slide movement has to assist in the cocking of the striker. The LEM can be said to be a true DAO because even whilst it has a cocking assist mechanism, the firing mechanism can still be fully tripped by the trigger pull only, albeit somewhat heavy then.

The key factor for a DAO is that the trigger function only can fully and independently cycle the firing action and fire the gun.

Glocks, Walther P99s da/sa etc. can best be classified as a DA/SA hybrid- any specific name you wish to call it is up to you.

Dave Sample
September 20, 2004, 04:53 PM
Very Good information and not a dumb question at all. I love the simplicity of the old 1873 type single action six shooters. It is very hard to have an AD when you have to pull that hammer back to full cock and then light it up. I also prefer SA 1911's because the DAO requires a combination of a sight picture disturbed by pulling the hammer back with the trigger. Cops are, for the most part, very poor gun handlers, and a double action revolver pointed at a perp with the hammer cocked back is a lawsuit waiting to happen. They are very sensitive in this mode and can be fired with a very light pull on the trigger. A cop filled with adrenalin pointing a gun at a suspect in the SA Mode is something that is a very dangerous combination. This is the reason for the DAO revolvers and I think a valid solution for street cops who have to carry PC revolvers due to the politics of Law Enforcement. The 45 ACP on my duty belt was just one more thing I had to tote around my waist and another part of The Badge of Authority that we had when "On The JOB". I was quite happy with my Model 58 S&W there also, as the .41 magnum had plenty of stopping power for me. I did not point guns at people, though. I just un-snapped the thumb break and if the gun needed to come out, it came out fast and went BANG. I still do not point guns at people, by the way. I may show them one to avoid an incident, and so far that has worked pretty good. Just my personal opinion and I am sure many cops will say I am full of it, but I am not in jail. And I could have been several times for a wrongfull death. Loaded guns are very dangerous, and if I have to use it, I do not want it to be an accident!

JohnKSa
September 20, 2004, 10:48 PM
jc sez,The Glock is actually a true DAO handgun. John repeats,For some reason, in spite of the obvious differences between a typical DAO and the Glock action, there are those... who insist on calling it a DAO. I suppose there's no harm in it as long as one understands what's going on inside the pistol. jc sez,There are revolvers that do NOT have the capability "to cock the hammer and fire SA" as stated. Ruger, S&W and Taurus make models that are DAO John repeats,Then, someone got the bright idea that it might be beneficial to have a double-action gun that DIDN'T have the SA capability. The trigger cocks and fires the gun with a single pull, but the hammer can't be cocked for SA functionality. These guns are called DAOIt's important to remember that the terms SA, DA, DAO all originally referred to revolvers and the way they function.

Some autos--notably the Glock--function in a manner that is not completely or accurately described or modelled by any of the above revolver actions.

The Glock trigger both compresses and releases the striker spring. That's like a DA (or DAO) and clearly UNLIKE an SA.

But, the slide action must partially compress the spring and reset the action before the Glock trigger can do anything. That is UNLIKE a DA or DAO revolver in which the trigger needs no external help to cock and fire the pistol. In this respect it behaves a bit like an SA although it clearly isn't. It can't be SA since an SA trigger doesn't compress the hammer/striker spring.

So, it is like and unlike an SA action. It is also like and unlike a DA/DAO action. Since it only has one functioning mode, it's clearly not a DA/SA.

Oddly enough, I suspect this is why GLOCK chose not to call it any of the above. ;)When a Glock sets the striker, it does so primarily as a safety measureOk, that's not totally incorrect, but it would be just as correct to say that it does so because the trigger can't pick up the striker unless the slide sets it.

In the partially cocked position, the striker nose is NOT "just behind the breechface". A little fiddling with a Glock will show that the slide compresses the striker by about 7mm. The trigger pull finishes the job with another 4mm or so.

Clearly, the slide's contribution to the striker spring compression is significant. It's true that the slide doesn't compress the striker spring enough to fire the pistol--BY DESIGN! The intention of the Glock designers was to construct a pistol which did not store enough energy for firing unless the shooter contributed more energy in the form of a trigger pull.

jc2
September 20, 2004, 11:17 PM
Oddly enough, I suspect this is why GLOCK chose not to call it any of the above.
That's right. In its technical material (versus its PR stuff), Glock calls it a "continuous double action" (read DAO). Sounds to me like Glock insists on calling it a DAO (despite some minor differences).

JohnKSa
September 20, 2004, 11:29 PM
Hmmm... would the armorer's manual qualify as "technical material"?

Cover Glock Armorer's manual:
Glock Semiautomatic "SAFE ACTION" Pistols (publisher's emphasis & quote marks)

Page 3 Glock Armorer's manual:
GLOCK "SAFE ACTION" PISTOLS (publisher's quote marks)

Page 5 Glock Armorer's manual, Paragraph 1:
...the GLOCK pistol has an action which combines the best characteristics of the traditional double and single action pistols, creating what has become known as the "Safe Action" system. (publisher's quotes)

My Glock manual also has numerous references to Safe Action system but never uses the term "double action". It also refers to the action as being "half-cocked" or "semi-cocked" by the slide.

The armorer's manual does makes a reference to "...simplicity of revolver-like operation with a constant double-action trigger pull..." in the paragraph immediately following the one I quoted from on page 5. I think that must be what you're referring to. But the manual clearly doesn't say the pistol is "continuous double action". It says it has a "constant double-action trigger pull." Your quote implies that this is a definition of the Glock system--seeing the correct quote in context makes it clear that it's actually describing the Glock trigger as having a consistant pull (as opposed to having a DA/SA transition between the first and second shot.)

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