Glock Striker Travel: Single- or Double-Action?
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  1. #1
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    Glock Striker Travel: Single- or Double-Action?

    Recently a Member posted the eternal question: are Glock pistols are Single Action or Double Action? Well, maybe it's not THE eternal question, but it's one we hear regularly. I gave the question some thought and decided to measure the striker travel. Maybe knowing something about that would help me to accurately describe the Glock trigger action in terms that most shooters would understand.

    To review, typically in a Single-Action semi-auto pistol, pulling the trigger pushes against a sear, which in turn releases the hammer to fire the weapon. The hammer is cocked independently of the trigger, typically by cycling the slide, but it may also be cocked manually in most cases. Familiar examples of Single Action semi-auto pistols include the 1911 and the Browning Hi Power.

    Typically, in a Double-Action semi-auto pistol, pulling the trigger on the first shot (when the hammer is in the fired position) first cocks the hammer and then releases it to fire the weapon. On subsequent shots, the pistol fires in Single-Action, since it is cocked by the cycling of the slide. Examples of Single Action/Double Action (SA/DA) pistols include the CZ 75, most Sig Semi-Autos, the Walther PP, HK P2000, and the Beretta 92FS. The most common DA only (DAO) pistol I can think of is the Ruger LC9, and there are Sig variants that are DAO.

    Where does Glock fit? Well, somewhere in between the two, actually.

    As we know, when the Glock slide is cycled, it partially cocks the striker spring by pushing the nose of the striker against the (temporarily) stationery trigger bar cruciform. Pulling the trigger back further cocks the striker by pushing back on the nose of the striker until the trigger bar is pushed down by the connector to release the striker, and the pistol fires.

    The nose of the striker has three positions when correctly installed in the pistol:

    1. Fired, fully forward
    2. Partially cocked, when the slide is cycled
    3. Fully cocked, just before firing, when the trigger is pulled all the way back

    I was able to measure the travel distance of the striker nose (and therefore the entire striker) by using the Orange Half-Height slide cover plate, used for inspection only. For the curious, this is part number SP 05865, and is readily available from Glock aftermarket suppliers.

    Name:  Rear of Striker Nose.jpg
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    Using this cover plate allowed me to insert a caliper with a depth gauge attachment into the back of the pistol, noting the depth from the back of the cover plate to the back of the nose of the striker.

    Name:  Striker Travel Measuring.jpg
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    Here are the measurements:

    1. Fired, fully forward: .726”
    2. Partially cocked, when the slide is cycled: .405”
    3. Fully cocked, the rearmost position of the striker: .270”

    Please note that these measurements are approximate, I did not use a fixture to hold the caliper or the pistol in place, and my hands probably shake a little.

    So, what does all of this tell us?

    1. Cycling the slide cocks the striker .321”
    2. Pulling the trigger cocks the striker the final .135”

    Total travel of the striker is .456”. Since 70% (.321”) of the travel occurs during cycling of the slide, and only 30% (.135”) occurs during the trigger pull, it seems fair to me to describe the Glock as a Single Action Biased, striker-fired pistol.

    Of course, others will differ!

    To see this in action, here’s that excellent Glock animation again: Glock Pistol Animation

    Chris
    Last edited by cohland; 10-07-2013 at 09:48 PM.
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  2. #2
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    "Single Action Biased, striker fired pistol."
    I think you've officially coined a new phrase, Chris.
    Being an old-timer, I look at any pistol on which, when the trigger is pulled rearward, the striker or firing pin is first moved to the rear, is a double action. Even if it were only 0.005". That's probably because I am overly sensitive to the politics of firearms nowadays. If the gun grabbers ever learn the difference between a magazine and a clip, they may someday be able to understand what single action and double action mean. [sarcasm ON] And of course, SINGLE ACTION PISTOLS ARE MUCH MORE DEADLY than double action pistols that require two motions in separate directions before they can be fired. [sarcasm OFF]
    -Blue

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    Great post Chris. As always your attention to detail is superp. There is a lot of great information in your post.

    I have always described the action of a Glock as falling in the none of the above category. As a technician by trade I tend to look at things in black and white. It works or it doesn't. Its on or off, 1s or 0s, etc.

    Labeling the Glock as Single action only doesn't pass my test because it completes the cocking of the striker and disengages the safety. For instance an old Colt SA revolver. Pull the trigger the hammer falls, that is it. Nothing more nothing less.

    It doesn't pass the double action test because the striker is already partially cocked. You can look at a DA revolver, you are completely bringing the hammer and action from the fired position all the way through the trigger pull to the point of sear disengament. That isn't the case with a Glock.

    If I had to pick the "best choice", I would lean towards DA, but I avoid that generally. When I am asked whether a Glock is SA, DA, OR SA/DA, my answer is "No, it is a Glock Safe Action".


    Chris
    Last edited by Tactworld45; 10-07-2013 at 06:58 PM.
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    Excellent description and work.

    "Single Action Biased" I like it! Accurate and direct.

    Gaz

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    Quote Originally Posted by OHgaz View Post
    Excellent description and work.

    "Single Action Biased" I like it! Accurate and direct.

    Gaz
    Thanks, I'm glad you liked it.

    Chris
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    This is not a knock on my friend Chris' work detailed above, it's excellent. But Question #4 on the Glock Advanced Armorer's pre-test and #5 on the actual exam was:

    "The Glock trigger mechanism functions in which of the following ways"
    A. Single Action
    B. Single Action/Double Action
    C. Double Action

    The answer is C. Double Action
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    Intereresting reading, thanks for working on that interrogation and sharing it.

    I read in the web a couple days ago that when comparing safety between glock and s&w, s&w made a study and glocks fired 100% of the time when partially cocked (62%? Of sear engagement), can we assume that partially cocked is the "same" as fully cocked ?
    I'm talking about safety.
    Last edited by lefty; 05-25-2016 at 03:03 AM.

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    Can you post the link where you read that information ?



    I am unclear on the definition of partially cocked.

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  10. #9
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    I read it in a board, there was not link only someone that said it, so I take it with a grain of salt.
    I tried to find the link but I did find it, my telephone bugs a lot, the web navigator shuts down very often . will try to find it today.

    Me too I don't understand well the partially cocked in striker fire guns.

  11. #10
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    I think the term "partially cocked" leads people to envision a hammer/sear system (at least me) which can give a wrong interpretation.

    When the slide cycles, reseting the trigger happens when the firing pin lug re-engages the rear of the trigger bar and forces the trigger forward. This force comes from the firing pin spring being compressed.

    To ensure the trigger moves all the way forward to 1)engage the trigger safety and 2)keep the trigger forward enough so the trigger safety doesn't bind against the frame, there must remain positive forward pressure from the firing pin spring - it can't fully decompress.

    I guess how much compression remains could vary from mfg to mfg. that was using the same method.

    To test if there was enough force to discharge a round from this point would require completely disabling two of the three Glock safeties, the firing pin safety which blocks the pin from being able to strike the round and the drop safety.

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