How Does the P7M8 Firing Pin Block (Drop Safety) Work?
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Thread: How Does the P7M8 Firing Pin Block (Drop Safety) Work?

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    Default How Does the P7M8 Firing Pin Block (Drop Safety) Work?

    I have come to the point where I want to make sure I entirely understand how the P7M8 operates, soup-to-nuts, as I will be carrying it. I aught to know how the thing works if I'm trusting my life to it; I aught to understand how it keeps things from going wrong and what things can happen to force something to go wrong. Moreover, I'm in a technical field, and I'd look like an idiot if someone asked me something simple about how the gun I carry works and I didn't know the answer . I have spent a good deal of time reading up on the action and examining/toying with my pistol disassembled to think about what each part does. I have learned a great deal, but there is one thing I can't quite figure out: the drop safety.

    As I understand it, the primary thing keeping the gun from going off when you decock it is the sear. Even when all the way forward, the sear holds the firing pin back enough so that it can't move out of its hole and engage a primer. The secondary firing pin spring holds it back this same amount at rest, but that spring could be overcome were the sear not also in the way, as it is when firing. The trigger can only disengage the sear all the way at the back (when you want it to), so the sear spring ensures that the sear will be engaged when it is at the front (decocked). In theory, you could imagine thinning the sear down a hair, perhaps from being slammed forward from decocking a lot, and if I understand everything correctly this would (in the absence of the drop safety) make the gun fire whenever you decock it, basically turning the P7 into a hand grenade with no pin. However, thankfully there is an extra thing keeping the firing pin from hitting the primer: the drop safety! At first I thought that the drop safety just introduced extra spring tension on the sear when it was cocked, but I realized that this was silly and would make the safety functionless at any time when the sear was not cocked up to it.

    So, how does the firing pin block/drop safety work? I realize there is two designs. I am most interested in the new one, but would also like to know how the old one works for comparison.
    Last edited by dove; 10-25-2012 at 03:44 AM.

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    The P7 firing pin has a flange on it.



    The bottom part of the drop safety catch blocks this flange, preventing the firing pin from moving forward.



    When the cocker is squeezed, the flange is engaged by the sear, pulling the firing pin back against the firing pin spring pressure. When the trigger is pulled the sear lowers pulling the drop safety catch down against the pressure of the drop safety spring. This allows the the flange room to move past the bottom part of the drop safety catch into the 'U' space of the drop safety catch when the the firing pin flange is released from the sear. Thus the tip of the firing pin can now move far forward enough to strike the cartridge's primer.





    When the cocker is released, the drop safety spring pulls the drop safety catch back up, and the bottom part of it again blocks the firing pin flange.

    As an aside, the drop safety spring is probably the most likely part to break on a P7, especially if you dry fire a lot. When it breaks, the drop safety catch comes loose, because the only thing attaching it to the slide is the drop safety spring. This sometimes jams the gun completely when it gets caught between the slide and the frame, and sometimes the drop safety catch flies out and is lost (which is probably better if you're firing in self defense because the pistol works without the drop safety catch, it's just less safe).
    Last edited by bigdave24; 10-26-2012 at 05:24 AM.

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    Thanks Dave!

    I'm still not 100% clear on everything, but this is progress! I don't have my gun in front of me to think about this physically but let me ask a few questions to try to tease out some more understanding:

    - What component is responsible for pulling down the drop safety catch? If the flange on the sear is all the way back and cocked (together with the flange on the firing pin that it is holding cocked), I don't see how it could be also in contact with the drop safety catch (which itself is presumably at the front where the firing pin flange would be at rest).

    - How did the 3(?) iterations differ? I'm looking at the sketches you show, but without a 3d diagram I can't see any functional difference between them. Moreover, I can't see any difference in the diagrams for the 85-87 and 87+ versions.
    Last edited by dove; 10-25-2012 at 05:54 PM.

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    The sear is the only part of the lower gun that could possibly engage the drop safety catch. It engages it when the trigger is pulled, thus lowering the sear. I edited my other post to make this clearer.

    The circled part on the diagram is what was changed from the previous iteration. I believe each change strengthened an area that was prone to failure.
    Last edited by bigdave24; 10-26-2012 at 05:26 AM.

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    Quote Originally Posted by bigdave24 View Post
    The sear is the only part of the lower gun that could possibly engage the drop safety catch. It engages it when the trigger is pulled, thus lowering the sear. I edited my other post to make this clearer.

    The circled part on the diagram is what was changed from the previous iteration. I believe each change strengthened an area that was prone to failure.
    Thanks, I got it now! Thanks for the clarification regarding the trigger pull; having just taken my gun apart and inspected it, I was going to ask about that. The reason I couldn't picture the sear doing it was because I was overestimating all the distances in question. Taking a look at it first hand made it all clear though. If I've got it correct now, *both* the sear and the drop safety catch are in contact with the firing pin flange at rest and together they redundantly prevent the firing pin from moving forward. I also see that it's a little tab sticking off the front of the sear flange that is responsible for pulling the safety down.

    Now, there is one thing that is bugging me. When everything is at rest, the sear is all the way forward and will block the firing pin from moving forward. However, you can check for yourself that you can pull the sear down with a finger nail (grips off) enough to clear the firing pin flange. You can't pull it down any further because the front arm of the sear comes in contact with the top part of the trigger mechanism. So, if for some wild reason the drop safety failed and the sear spring broke, there would be nothing keeping the firing pin at bay.

    This is just a silly, unrealistic, pathological example, but the only reason it bothers me is because it could have been very simply and elegantly avoided. If you look at the top side of the front arm of the sear, it looks like it was cut to shape to the bottom edge of the top part of the trigger mechanism, however it falls short of meeting it. If they had extended the metal here so that this top part of the sear arm nearly met the trigger part, then there would be no way for the sear to lower when it was in the decocked position. Doing this would have no functional drawback that I can see, and would not require much metal. Doing this would ensure that even in the event of sear spring failure, the sear (when decocked) would always be forced to stay high enough to block the firing pin.

    The question is: why didn't HK incorporate this simple design element? Am I missing something? I have no experience with gun design, or even mechanical engineering in general, and this is the first gun I've ever studied, so I can't imagine that I'm the only one to have thought of this. Yet, I can't see how they could justify not incorporating it if they did think of it.



    EDIT: Oh and I can see what you're talking about on the diagrams now. The 85-87 version looks like it beefed up the part that the sear pulls on, and the 87+ version looks like it beefed up and smoothed the fillet on the part the firing pin flange falls into. On an unrelated note, I heard a story that the drop safety was updated due to an officer that dropped the gun at some weird irreproducible angle and had a AD. Is this true? And if so, how the hell did the gun go off if it was out of his hand (presumably decocked) and the sear was in the way of the pin?

    EDIT 2: Nevermind about the story, got my answer here https://www.hkpro.com/forum/hk-refere...ety-parts.html. Now what G3Kurz didn't mention is why the old drop safety failed in that scenario. In any event, I should draw attention to the fact that my proposed modification would have made that scenario impossible, even in the event of drop safety failure.
    Last edited by dove; 10-27-2012 at 05:37 AM.

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