From another thread...

Single Action Only (SAO or SA):

Your two most common types if SAO guns are 1911 pattern semi-automatics and your "Western" revolvers" such as the Colt Single Action Army. A lot of people get confused on this as they mistake action type and trigger type. With both the 1911 and single action revolver, the hammer must be cocked in order for the gun to fire. Pulling the trigger causes one action, that of the hammer to fall and make contact with the firing pin. Looking at this example, the 1911 is cocked by the cycling of the slide after being fired; hence it is a semi-automatic, but still a single action trigger. The single action revolver must be cocked manually for every shot. To confuse you even further, there are some single action only guns that are striker fired as they are fully cocked by the manual cycling of the slide or other operation. Two examples of single action, striker fired guns are the HKP7 family and the Springfield XD (includes XDM) line. There are some that will disagree and say that striker fired guns are not SAO. But looking at the requirement that pulling the trigger facilitates only one action, the release of "X" that initiates the firing sequence, YES they are single action and are even considered SA by the International Defensive Pistol Association (IDPA).

Double Action (DA):

Most modern revolvers are referred to as double action, despite the fact that they are still capable of being fired in the single action mode, why this is I don't know. Double Action indicates that pulling the trigger caused two actions, 1: the cocking and 2: release of the hammer. One action=two results. Common double action revolvers are the Ruger GP100 and Redhawk models.


Double Action Only (DAO):

DAO guns can not be manually cocked; they are cocked and released by trigger manipulation. DAO guns can be revolvers or semi-automatics. Glocks are erroneously referred to as DAO as the trigger must be pulled to fire the gun, in my opinion this is false. Glocks and many other makes/models are partially cocked, striker fired guns but we’ll get to them later.

A DAO gun has the following traits.
1: Is only cocked by trigger manipulation and the trigger pull is the same for every shot.
2: In semi-auto guns, the hammer will go back to rest (hammer down behind the slide) after each shot. Remember, the trigger cocks and releases the hammer, not the slide in this case.
3: As the trigger is the driving force to cock and release the hammer, second strike capability is there. If you have questions on second strike capability...try Google, I'm not covering that in this piece. Common DAO guns are the S&W 642 and KelTec P3AT.

There are some different types of DAO, such as DAK and LDA from Sig and Para Ordnance respectively; I will cover those in brief at the end.

Traditional Double Action / Single Action (DA/SA):

This type of trigger is what is found on the Beretta M9 and other semi-automatic pistols. The first shot can be double action or single action IE one pull of the trigger will cock and release the hammer. If the hammer is manually cocked, pulling the trigger will release the hammer. As the M9 is a semi-automatic pistol, the slide will re-cock the hammer after the gun is fired. With a DA/SA type of gun, all subsequent shots will be fired single action until shooting stops and the hammer is de-cocked.

Partially Cocked, Striker Fired / Striker Fired:

Glock, Kahr, some S&W models and others operate on this type of mechanism. What sets these aside from DAO guns is that the cycling of the slide partially cocks the striker and the pulling of the trigger finishes cocking the mechanism and releases the striker to make the gun go bang. Remember what I said before, some striker fired guns fall into different categories. Glocks and the like kind are generally referred to as being DAO and it is common to see the term associated with them. Personally, I don’t view them as DAO, but the Bureau of Alcohol Tobacco and Firearms (ATF) did, which is why it’s kind of stuck. However, a DAO “X” and a Glock have very dissimilar traits and the triggers have different feel which is why I separate them in this text.

Now that we have the basics out of the way, we can take a look at some different "sub-types" of triggers. As mentioned previously, out there in the world there are these two strange beasts that are called Double Action Kellerman (DAK) and the Light Double Action (LDA) which are found on so equipped Sigs and Para LDA models.

Per Wikipedia:

“SIG released an altered version of the double-action only (DAO) pistols called the DAK (for Double Action Kellerman, after the designer of the system). The DAK capability is available in 220, 226, 229 and 239 models. When firing the pistol the first trigger pull is 6.5 lbs (compared to 10 pounds for the standard DAO). After the pistol fires and the trigger is released, the trigger has an intermediate reset point that is approximately halfway to the trigger at rest position. The trigger pull from this intermediate reset point is 8.5 lbs (38 N). If the trigger is released all the way forward, this will engage the primary trigger reset and have a trigger pull of 6.5 lbs (29 N). To engage the intermediate reset, the trigger must be held to the rear while the slide is cycled, either manually or by the recoil of a round being fired. The United States Coast Guard has adopted this firearm as its PDW (Personal Defense Weapon), replacing the older M9 pistol.[9]”

As there are two different pull weights, this is not a conventional DA.

Para LDA:
Without going into gross detail, the LDA is a super smooth, lightweight trigger. Generally speaking most DAO guns have a heavy pull and no safeties. The Para LDA incorporates the 1911 pattern thumb safety thus allowing for a very light pull but still has the hammer going back to rest after every shot, but if I recall correctly, the LDA has no second strike capability and needs the slide to cycle in order for the trigger to do it's thing in cocking and releasing the hammer.

HK refers to their DAO as LEM (Law Enforcement Modification) which is thought to be another form of lighter double action, but it is really another pre-cocked hammer system, you can read more about it at HK's website.

It's a lot of info to take in. Each method has its advantages and disadvantages. If you'd like to read more on the types of trigger actions on semi-autos, I would definitely recommend checking out Automatics: What Action Type for Me? by Stephen Camp.

The majority opinion on triggers is that it’s better to have only ONE trigger pull to master, such as from a SAO or DAO gun rather than having to master two distinctly different trigger pulls such as what would be found on a traditional DA/SA gun like the Beretta M9. I fall in with those that feel one trigger pull is best, however with the proper training and time spent mastering both trigger pulls, there is nothing wrong with a DA/SA gun.

4: With or Without External Safeties

There are those that love them, those that hate them, and those that are undecided.

I like an external safety for the following reasons.

A: As we now have a child in the house, if he ever does get his hands on a loaded gun, there are a couple more steps to achieve ignition other than just pulling the trigger. I know what you’re all thinking, “That would never happen” but things do happen that shouldn’t.
B: In the event that someone gets my gun during an altercation, and they don’t know how the gun works, that gives me a little more time to do something. Again, I know what some of you are thinking, but I’ve had at least one police officer and one range buddy demonstrate that they didn’t know how to work a 1911 and one gun shop employee demonstrate that he didn’t know how to operate a HK P7.
C: Most of the guns I have are single action and have light triggers; the external safety prevents a negligent discharge in the event of improper handling provided that the safety is engaged and functioning

The camp that does not like the safety uses the following as their main argument.
A: You (this really means them) will forget to disengage the safety in a time of stress.
B: It is faster to not have to fiddle with the safety.
C: It’s just not needed.

Regarding speed, it’s a training issue, not an equipment issue. If you train to disengage the safety at the correct time, you won’t forget it and it’s just as fast as not having one.

It’s a personal preference, but if you decide that you want a firearm with an external safety you better practice, practice, practice. The safety should be disengaged during the draw stroke and should be “off” when being presented to the target”

I carry a Beretta Cougar DA/SA with safety on, one in the chamber. I practice disengaging the safety, so that it is part of drawing. Practice is the key.

Originally Posted by ccm

...Seems to me that unless your weapon has a double action only trigger you must have a safety on the gun. If you were to ever have to use the weapon it seems to me that a safety is just one more thing to get in the way of quick deployment...

That's my feeling about the subject too.
My 24/7 pocket-carry pistol is DAO for the reason you state, plus that I don't have to worry about the safety lever being accidentally wiped into the "off" position.

However, to be completely honest, my "serious social situations," OWB-carry pistol(s) are all SA with safety levers. (Where I live, a special case, it's easy to determine in advance which kind of gun will be required.) The holster(s) I use are made to control the safety lever and to resist its movement.

Originally Posted by Steve M1911A1

That's my feeling about the subject too.
My 24/7 pocket-carry pistol is DAO for the reason you state, plus that I don't have to worry about the safety lever being accidentally wiped into the "off" position.

However, to be completely honest, my "serious social situations," OWB-carry pistol(s) are all SA with safety levers. (Where I live, a special case, it's easy to determine in advance which kind of gun will be required.) The holster(s) I use are made to control the safety lever and to resist its movement.

How do you feel about DA/SA? Since the first trigger pull is the longer one would you still consider it equal to the DAO safety wise? I know the learning of the two separate pulls is a negative for some people, I am thinking purely safety.

Originally Posted by VasSigmeister

How do you feel about DA/SA? Since the first trigger pull is the longer one would you still consider it equal to the DAO safety wise? I know the learning of the two separate pulls is a negative for some people, I am thinking purely safety.

The safety of a DA/SA, compared to that of a DAO, depends on whether the gun is equipped with a decocking lever. There is a considerable margin for error in letting the hammer down on a live round, manually (no de-cocker). I do it all the time with my CZ's, but I am well aware of the possibility of letting the hammer slip some time and firing the chambered round, and I am extremely careful when I do it.

Once the hammer is down, though, your first shot is just like with a revolver or DA pistol. I consider striker fired, polymer framed pistols to be the best, in general, for concealed carry.

I, personally, carry a single-action 1911, cocked and locked, much of the time during cool weather, because I have trouble finding a compact that will fit my long trigger reach properly. The CZ RAMI fits, but is almost as heavy as a 1911. I may eventually settle on something like a Walther PPS, if the interchangeable backstrap will make it fit my hand properly.

Originally Posted by VasSigmeister

How do you feel about DA/SA? Since the first trigger pull is the longer one would you still consider it equal to the DAO safety wise? I know the learning of the two separate pulls is a negative for some people, I am thinking purely safety.

I have to selectively echo Jeff Cooper here: The Traditional Double-Action (TDA) semi-auto pistol is a solution to a problem that doesn't exist.
There's a good reason for the DAO action, and for the SA action too, but all the TDA action does is complicate your life. It presents you with two different trigger pulls to learn, and to switch between when you have other, more pressing things demanding your attention.
Further, the whole idea of a hammer-dropping safety makes me shudder. All that stands between a hammer-dropping safety and rampant disaster is what one hopes is the correct heat-treatment metallurgical system. Back at the end of WW2, GIs brought home Walther P.38s that had been assembled under less than perfect conditions, and the owners of those prizes experienced some pretty horrific NDs when the imperfectly-heat-treated firing pins and safety spindles of those P.38s failed.
(Even when correctly heat treated, steel can still crystallize under repeated stress and give way. Yet we are led to believe that the mechanical hammer-dropping safety is a safe way to render a gun safe. Hmmm...are you also interested in a government-run health plan?)

Oh I see, thanks guys I was just curious as to your views on the matter, makes sense, and I will try to remember all of that!

And I am not very fond of the idea of a gov't run health plan, but that is a convo for a different thread!

...It was a rhetorical question related to the efficacy of the hammer-dropping safety on our government-issued service pistol.

Originally Posted by Steve M1911A1

...It was a rhetorical question related to the efficacy of the hammer-dropping safety on our government-issued service pistol.

Haha I made that connection, I was just throwing it in there.

I go with a strait DA trigger like on Glock and similar. Because all shots are DA I can depend on where the round will hit my target. I used to be a dedicated DA/SA guy, but was only consistent with the SA feature. I always shot too low on the first, long DA pull. Nothing wrong with DA/SA as long as you are aware that the first shot may not hit at POA and you may need to get a second shot off immediately.

A related note that I did not notice being mentioned has to do with trigger pull. For a concealed handgun I prefer to have a trigger pull in the 8 lb plus range. I've found I can flinch off shots if the pull is 5 lbs or less when rapid firing or feeling anxious. My preference for a heavier pull could be related to the fact that my fingers are fairly strong too since I play at the piano and guitar. YMMV

...And I play the 5-string banjo.
The extreme delicacy required of my fingers, to get the nuances of sound from my instrument, has trained me to use a very light trigger pull.
As a string player, I'm sure that you understand just how delicately a 5-string banjo must be played.