The shooting community is blessed (or would that be cursed?) with acronyms. Unfortunately, these acronyms bandied about have great implication about the nature of the trigger in a gun. The trigger ‘train’ is commonly referred to as the ‘action’. Some are the same thing with a different name, some seem to work just alike and are considered a different action.
If it were just terminology, there wouldn’t be a problem, but unfortunately, the acronymic descriptors loosely define what we can expect from the ‘action’. You’ll see why I say loosely pretty quickly.
Like my thread about trigger characteristics, this addresses SD (self-defense) guns, not gaming guns, although in the case of action types it doesn’t matter if it’s a SD gun or a competition gun. Let’s start where it starts, with the SA (Single Action).
SA – Single Action and SAO – Single Action Only:
In the beginning,……….well, let’s at least jump ahead to the SA revolver. A SA revolver was an early ‘repeater’, i.e. could fire a number of shots, before needing to be reloaded. The SA revolver has a trigger and a hammer. I realize some of this may seem trivial but it is nonetheless essential in understanding more ‘complicated’ SA guns.
First let’s clear this up: SA and SAO mean the same thing. SAO may better emphasize that this is the only way a gun can be shot, but that is also at least implied by SA.
To shoot the SA revolver, one would cock the hammer manually, which would rotate a fresh round under the hammer, and then when the person was ready to shoot, he would pull the trigger to ‘drop’ the hammer. The trigger only did one thing, release the hammer, hence the term Single Action. So the defining feature of the SA is - the trigger does one thing, drop the hammer. The gun fires and remains inert unless the hammer is manually cocked again.
Sticking with SA, let’s move to semi-autos. The trigger in a semi-auto can and only does one thing - guess what? Drop the hammer. In the revolver, the hammer had to be cocked by hand prior to each shot. In the semi-auto, the recoiling slide cocks the hammer after every shot, and unlike the revolver, the semi-auto leaves the hammer always cocked and ready to fire. Since SA triggers tend to have relatively short trigger pulls, something would have to be done to make the gun secure. This can be accomplished two ways. One, the hammer can be lowered carefully by hand, which some consider dangerous since if the hammer slips, it fires the gun and two a safety can be engaged which blocks the trigger from firing the gun.
So how does one carry a SA semi? Well, most commonly in what’s known as ‘cocked and locked’. For the semi-auto handgun, this means there is a round in the chamber, the hammer is cocked, likely from ‘charging’ the chamber, and the safety is engaged. It would be assumed that a full magazine is in the gun.
BTW, it is a magazine not a clip. A clip is, as the name implies, a clip that holds bullets together for insertion into the magazine of a gun. A magazine holds the rounds and feeds them into the action. Probably the most well known clip is that of the Garand rifle. The Garand rifle has a non-removable magazine that is ‘charged’ or loaded via a clip.
Anyway, we got to a cocked and locked SA handgun so how does one fire the cocked and locked SA. Generally, the thumb of the gun hand swipes off the safety which enables the trigger to fire the gun.
Some examples of SA guns are the 1911, Browning High Power, and a much more modern design the Hk USP. The latter isn’t limited to SA and the cocked and locked mode, and can be carried and fired as a DA/SA with a decocker, more about this unique gun later.
The addition of the safety on the SA adds a complication to the user. He must manually apply the safety when he no longer intends to shoot the gun. Under stress he may not remember to engage the safety. Worse, a casual user, may not remember to disengage the safety in a life and death situation.
With training/practice (they are not the same) the safety disengagement and re-engagement can become second nature. Although, even with seasoned shooters, I have seen them miss the safety on a draw and fire and seen them holster with the gun cocked with the safety off. Ok, some examples of SA guns:
First and foremost the most popular gun in the world, the 1911 is a SA only gun with a thumb safety to make it safe while loaded and cocked. It has a very short, light trigger with a pull weight of anything from 4 lbs to probably 6 lbs.
Then a couple of not-so-obvious SAO guns – the Springfield Armory XD and the S&W M&P, and there are others, they all are unique in some way, yet alike in function of the action. You’ll see later on that a Glock is a bit different than the XD and M&P. The XD action is called the Ultra-Safe; the M&P action doesn’t have a trade name.
BTW, I couldn’t get the S&W website, but Bud’s list the M&P as a DAO. I know this is gonna sound awfully bold, but it is not DAO, it is SAO. When the slide is racked and released on an M&P, as the slide returns forward, the tab (or sear) on the striker which is housed in the slide, is stopped by the sear in the housing. The sear in the housing is mounted on a pivot and cannot move other than pivot very slightly. Sooooo, the striker spring is fully cocked when the slide goes forward. When the trigger is pulled the sear is rotated downward which releases the striker under the force of the striker spring. How many things does the trigger do? Just one, release the striker, hence it is SAO.
The XD works the same way but with a bit different implementation.
So if the 1911 is a SA and it has a thumb safety, what about the M&P and XD? Well, they are SAO, but they have two things different, much, much longer trigger pull and a bit heavier too. Also the XD has a grip safety similar to a 1911. The M&P can be purchased with a thumb safety, it seems most people prefer the M&P without the thumb safety.
DA – Double Action
The DA revolver was the next development in revolvers. Guess why it’s called Double Action? The trigger does two things. It does everything the hammer did on the SA revolver, plus it drops the hammer. So, on a DA, the trigger actually rotates the cylinder, cocks the hammer, and releases the hammer in one stroke of the trigger! That sounds like a triple action doesn’t it? But, there’s more!
The DA revolver can be fired in a SA mode as well, just by manually cocking the hammer! SA mode always has a relatively light, short trigger stroke that many prefer over the long, heavy DA trigger. In the DA mode, the trigger has to rotate the cylinder and cock the hammer against a pretty strong hammer spring – all that makes the trigger heavy. But if you manually cock the hammer, all the trigger has to do is release the hammer. The trigger pull weight in DA mode is typically around 10 - 12 lbs, that’s pretty heavy but manageable. It helps a lot if the trigger is smooth. A buttery smooth trigger can make a heavy trigger feel lighter. In SA mode a revolver trigger has a pull weight of something like 4.5 lbs, which is pretty light. Clear to see why people would shoot better with the SA than the DA. Once the DA trigger is mastered however, one can do some impressive things with it.
Really, it would probably be more accurate to refer to this type of action as a DA/SA or a SA/DA, clearly indicating that the gun can be fired in two modes. But as far as I know the DA revolver has never been referred to as a DA/SA or a SA/DA. That brings us to the DAO.
DAO – Double Action Only
A DAO gun, be it semi or revolver is a gun that can only be fired in double action mode. For example, if you were to machine the hammer spur off of a DA revolver, you wouldn’t be able to manually cock it and you’d have a double action only mode.
If the DAO retains the long, heavy trigger pull, why would anyone want a DAO. Well it may not be as bad as I’ve made it sound. In the early days of Bullseye shooting, revolvers were used and they were fired in the DA mode. The idea here was that the DA mode releases the hammer and hence it has a shorter distance to fall to strike the primer. In SA mode, the hammer cocks in the SA sear and is considerably further back than the release point of the DA mode. Purportedly, there was less time and hammer motion to disturb the sight picture with the DA mode – at least that’s the way it was explained to me.
Further there were a lot of lawmen that were very fast with a DA revolver firing it in the DA mode. Perhaps the most spectacular was an FBI agent named Jelly Bryce. He could draw and fire his DA revolver in two-fifths of a second! And there were many others as well.
But again, if a DA will fire both ways, why not just fire it in DA if you like the DA mode? Well, there are a couple of problems. One, if a DA can be cocked, it’s gonna wind up cocked some how. One example of the problem was reported by Massod Ayoob. An officer was holding a suspect at gunpoint with a DA revolver in the SA mode. IOW, the hammer was cocked. Unfortunately, we humans suffer from sympathetic limb reflex or whatever it’s called. What it means is that if you do something with one hand, the other hand is affected. The officer clamped down on the cuffs, had a sympathetic reaction that fired his gun. Not good! As a result, a lot of PDs had all revolvers converted to DAO which is much, much more resistant to that type of thing.
Then, if you cock a DA revolver and don’t shoot it, how do you ‘uncock’ it? Well, you have no choice but to hold the hammer and pull the trigger, and carefully lower the hammer on a live round. The DAO avoids all the complications of safeties, decockers, cocked revolvers, and is very resistant to sympathetic reaction.
Lastly, if you were in a SD shooting, DAO eliminates any possibility of holding a gun on someone with a cocked hammer. Just think about that! In SA all it might take is a good startle and BANG! Second, let’s say you get through holding the cocked gun, now what are you going to do with it? It’s cocked. How do you uncock this thing in public? Wait till you get home? How you gonna carry it home? In the glove box? Cocked and holstered with the barrel pointed at your leg?
The DAO, be it revolver or semi-auto avoids these potential problems completely. There’s another advantage to the DAO too. All trigger pulls are exactly the same unlike some guns that we’ll discuss shortly.
The truly big asset to DAO guns is shear simplicity. They are the ultimate point and shoot, holster safely – whatever. Next some of DAO guns, some unique DAO mechanisms and the way they’re sometimes disguised.
DAO revolvers typically have no hammer spur, or the hammer is enclosed and completely inaccessible by the user. A number of manufacturers make DAO semi-autos, sometimes they are cleverly disguised but we’ll try to undisguise them.
Sig 226, 229, 228, and sigpros can be converted to DAO, I know because I’ve done that. Sigs 226, 229s are almost exclusively configured as DA/SA which I’ll denigrate shortly or as a DAK.
The Beretta 92FS are most commonly available as DA/SA but a DAO model, the D model is available. The Beretta PX4 is available in a DAO, but again most commonly configured as a DA/SA.
The Sig 226 and 229 is available in a DAK trigger configuration that is proprietary to Sig. DAK stands for Double Action Kellerman; Kellerman designed the trigger and the DAK trigger deserves a few words.
First the Sig 229 DAK won a huge government contract after prevailing handily in the ICE (Immigration Customs Enforcement – I think that’s the right name) trials. The DAK is more than just a DAO trigger – it is actually two in one. It has two double action modes, a long, light mode and a shorter, heavier mode. Why anyone would want something like that is beyond me – wait I have a 226 and a 229 with DAK triggers – well then I ought to know! One redeeming feature, perhaps, of the two-mode DAK trigger is that if you were to short stroke it, you might still get the shorter, heavier mode. That’d be a whole lot better than a complete short stroke.
A huge difference in the DAK trigger than say a revolver DAO trigger is two things: one it has just a wee bit shorter pull and a whole lot lighter pull, (can you say 50% lighter) than the typical revolver DAO or DA mode or the DA mode of a DA/SA trigger. The hammer that comes on a DAK version of the Sig 226 or 229 is bobbed, i.e. has no hammer spur and of course cannot be manually cocked.
The new kid on the block the Sig P250. The P250 is a true DAO semi-automatic, i.e. it was designed to only be a DAO. Obviously the design goal was to essentially put a DAO revolver-like trigger in a semi-automatic gun. There is one huge exception: it is far lighter and smoother out of the box than any DA revolver and the DAK versions although the DAK has a tiny bit shorter pull.
Now for some cleverly disguised DAOs as promised. First, the earliest and probably most debated is the Glock Safe Action. Safe Action is mostly a trade name, rather than a true action description. The trigger action of the Glock is often debated with the appearance of great authority. And it probably is debatable; I’ll explain how it works and you can decide for yourself. First, I’ll just note that the IDPA allows the Glock in the Stock Service Pistol category where DA/SAs and DAOs compete. OTOH, the XD and M&P are not allowed to compete in this category. The difference? The classification of the Glock trigger based on operation. Here’s how it works:
A Glock is a striker fired gun. That means it has a firing pin called a striker instead of a hammer. The striker, housed in the slide, has a tab, we could call a sear, that engages a crude sear on the trigger bar which is housed in the frame. The trigger, also housed in the frame, has a spring that pulls the trigger rearward, that’s right rearward – the trigger spring is trying to fire the gun! However recall the striker also has a spring that pushes the striker toward the front of the gun. When the slide is racked and released, the tab on the striker engages the crude sear on the trigger bar. The striker spring and the trigger spring act against each other which pull the trigger to its full forward position and the striker not quite to the end of its travel. And, that’s where the debate comes from. The action of the slide only partially cocks the striker, looks to me like to about 3/4 of its break position. So what gets the striker to move rearward more to the break position? Pulling the trigger! So the trigger first moves the striker rearward and continued rearward motion separates the two sears and the striker is driven forward by the striker spring into the primer of the bullet. What’s the nature of a SA trigger? It does one thing – break the shot. How many things does the Glock trigger do? While you’re thinking about that, I’ll move on to a similar conundrum with the LEM trigger.
Like the Safe Action is proprietary to Glock, the LEM is proprietary to Hk (Heckler and Koch). The LEM action is available on the Hk USP and the Hk P2000 and I’m not sure about the P30. The action on both the USP and P2000 are hammer fired instead of striker fired – they have an external hammer. I’ll describe the LEM on my P2000 and assume the LEM on a USP works the same but I don’t know that for sure.
OK, when the slide is racked and released, an internal ‘hammer’ is set. When the trigger is pulled the external hammer is rotated into the release position. The pull is quite light until the external hammer reaches the break point. At the break point, the trigger resistance increases dramatically and abruptly because both hammers are about to be released. When the shot is fired, the cycle repeats.
The gun is left with the internal hammer cocked and the external hammer down. This kinda seems like the cocked SA semi we discussed earlier, but the difference is the Hk P2000 has a much longer, albeit lighter trigger pull and then an even heavier pull at the break point. But it is a DAO action because the trigger has to move the external hammer just like the DA mode of a revolver and then if breaks the shot – two things. Next up, the DA/SA.
DA/SA – Double Action/Single Action
This only applies to semi-automatics even though as we’ve seen, a DA revolver can be fired both DA and SA. But the DA/SA can do something the DA revolver can’t. It automatically changes from a DA first shot, to SA only. So in a nutshell, the first shot out of a DA/SA is in the DA mode, and the next shot(s) is SA. The DA trigger mode is much like the DA of a revolver in that it is relatively long and heavy. Then, without warning, after the first shot, it goes into a light, short SA mode. When you stop shooting, the gun is left cocked in the SA mode. So to make it safe, you have to manually decock the hammer. Fortunately, most DA/SA autos have a decock lever, or decocker. When manually operated, the decocker drops the hammer without and danger of the gun being discharged in the process. But, just like the manual thumb safety on a 1911, the decocker of the DA/SA is an added complication.
I’ve shot these things for years and I personally feel these are the least desirable types of triggers on the market. They have a relatively long, heavy pull on the first shot and then that light, short pull on the next shot(s). This complicates learning the trigger, or I should say the two-in-one triggers. It complicates the handling of the firearm, and from what I have observed over many, many years, it promotes shallow, if not out right poor training habits.
Before I go on, let me say, the system works, but to truly deploy the gun as intended, it takes some dedicated, deliberate training. Just to prove the DA/SA system works, Ernst Langdon took a Sig P220 ST DA/SA, did some polishing on the trigger components, and beat Rob Leatham in a national competition and Rob was shooting his high dollar custom 1911 – SA for those of you that don’t know. But we aren’t Ernst Langdon and we don’t shoot 20 – 30 thousand rounds a year, and we don’t do the same level or dedicated training he does.
So back to the real world and why I say the DA/SA promotes some bad, even deceiving practice sessions. Here’s how I see many shooters train with their DA/SA guns. They get to the range, load up range ammo in a mag (magazine), shove the mag in the gun and rack the slide. Racking the slide cocked the hammer and put them in the SA mode. Most people run the magazine in the SA mode. A few may decock the for the first shot. They leave the range thinking how good they can shoot a DA/SA gun. But what about reality? Let’s say they’re caught in a situation where they have no choice but to draw and fire in a life or death situation. What’s the first shot going to be? DA! What mode do they rarely if ever, fire their gun? DA! When’s the first time they’re going to use DA? In a real life or death situation! Does that sound good?
Which is mode is more difficult to shoot in? DA. Which mode should be practiced more then? DA.
one of the most unique handgusn in the world
That leaves us with one unique gun to discuss, the Hk USP. The USP can be carried as a DA/SA or as a SA with the thumb safety on. This is a particular example of where there would be a distinction between SA and SAO. I cannot say the USP is SAO, because it can be fired and carried as a DA/SA also.
In the SA mode, i.e. hammer cocked, the Hk has a fine SA trigger, almost rivaling the 1911’s crisp break. OTOH, the USP has the worst DA trigger I’ve ever seen in a modern gun. It is not only long and heavy, it’s creepy and spongy.
Anyway the USP can be carried in essentially three modes – ‘cocked and locked’ SA, hammer down in DA/SA and hammer down and safety on in DA/SA mode.
The SRT refers to Sig's proprietary trigger reset modification. It shortens the trigger reset on the P220, 226, and 229 DA/SA guns. Note that the SRT is only for DA/SA guns. It has no application on DAK triggers or the P250 DAO trigger. I haven't tried one, but I hear good things about it. I am quite skeptical though, because I have also heard of premature discharges because the trigger is too easy to operate. Plus it applies to one of the worst trigger configurations on the market - the DA/SA and it does nothing for the DA mode that needs more help than the SA mode.
This is quite a controversial device. I’ve known police officers with years and years of service that will attest that the magazine safety or disconnect saved a number of lives in his department alone and further that they have never had a bad outcome due to them. Others, at best, have given one or two isolated cases where a magazine safety changed the outcome for the worst, or could have had the event actually occurred.
The Chattanooga PD has use S&W semi-autos for years and years and years and I have yet to hear of one negative outcome due to the magazine disconnect or safety. So what is this controversial thing?
It means, that if you remove the magazine from the gun, the gun cannot be fired even if the trigger is pulled and you have a round in the chamber.
One of the most common accidents with semis occurs when a person has forgotten how his gun works because he’s not a gun guy, but he removes the magazine thinking that unloads the gun, yet it still has a round chambered. He pulls the trigger to decock it or for whatever reason, or he hands it to a buddy that’s not a gun guy or not familiar with semis and rules and he pulls the trigger and BANG, the one in the chamber fires. That couldn’t happen with a mag disconnect aka mag safety.
The benefit of this feature may be a moot point since you can only get it on S&W pistols and the only S&W available at your gun store at the time may or may not have the magazine safety so you may have to take what’s there or wait a long time. Personally I like them and have them on both my M&Ps.