Hk usc trigger
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Thread: Hk usc trigger

  1. #1
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    Default Hk usc trigger

    I just have a few quick questions about the Hk usc trigger group. I’ve read on this sight and have observed for myself that the Hk usc does not have a disconnector. So if you look in the trigger group you can see this part that is called out as a locking lever that appears to catch a little tab on the back of the hammer when the hammer is in the cocked position. Then when you release the trigger the locking lever releases and the trigger resets and the sear catches the hammer at the base of the hammer in a little notch. It all seems pretty typical and straight forward. But when you remove the locking lever and you cock the hammer and hold the trigger down it stays all the way back and when you release the trigger it resets and is caught by the sear. It’s almost like the locking lever isn’t even doing anything. So I guess my question is what exactly is the part that is functioning like a disconnector In this trigger group because at first glance it appears to be the locking lever but something else is at play here and apparently I’m not smart enough to figure out hk’s over engineered over complicated triggers.

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    If the firearm was select fire, I'd say it was a rate reducer based on appearance and initial observation.

    The HK SL8 and burst G36 fire control groups used the same or similar locking lever.

    For the SL8, my best theory is it was a fairly unnecessary attempt to delay the hammer's travel a little bit as they do not have the hammer actuator (safety sear/auto sear) that all G36s have, even with the FBI semi auto fire control group.
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    The locking lever is used to reduce the trigger pull in the SL8 and USC. the SL8 and USC trigger groups are the same. This is noted in the patent documents (US patent# 6640479 B2) of the G36 Match trigger. The semi only G36 does not have the locking lever. I am not sure of the full use of the locking lever in a burst trigger group since I have never seen one. I need to read the patent on the burst trigger. (US patent# 6215735)

    The combination of the sear and slide is acting as the disconnector. In the G36 and UMP the Slide has a catch that moves the sear back in full auto so the hammer does not catch on it when the bolt goes back as long as the trigger is held. If you look at the sear, it has an oblong hole that allows it to move back and forth on the pivot pin. IN the G36 the hammer has a second tab that is stopped by the Actuator or catch during Full auto. The UMP also uses an actuator or catch. The USC does not have the cut out for the actuator. There is a good picture of the trigger group in the UMP armorers manual. Depending on the manual you read it may be called a catch, actuator or release lever.
    Last edited by CNADNSL8-5; 02-17-2020 at 05:21 AM.
    SL8/G36 (custom conversion), USC/UMP5 (custom conversion), HK45, P2000 V1, SPF9-SF, HK78, HKP2A1

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    I don't have a trigger scale to check, but the locking lever is indeed intended to reduce the trigger pull. It pushes down slightly on the bumps on the back of the hammer when cocked, and balances against the hammer spring. If you pull the lower off so you can see the internals, cock it and take the safety off. If you pry UP on the locking lever, you'll see the back of the hammer lift up ever so slightly. Drop the locking lever and you'll see the back of the hammer push down just that same little bit. The locking lever is pushing the hammer down that tiny bit, reducing the drag of the sear on the notch in the hammer.

    I can't really tell much difference in pull with my fingers, and have always been interested in checking one with a scale, but not enough to buy a scale. Ha.
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    Sounds about right - 12+ lbs for the UMP, 9.5 lb for USC (according to Shooting Illustrated). Either way, a heck of a heavy trigger pull.

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    “The combination of the sear and slide is acting as the disconnector. “

    I’m still kind of confused about how this is happening. By the slide I’m assuming you mean the bolt sliding over the trigger pack. I know kind of what your talking about because I’ve seen a video of how the trip lever works in a full auto with the bolt sliding over the top of the trigger pack. But if you cock the hammer and hold the trigger down and then let go there is still a reset which is indicating a disconnector function and this happens with the lower removed from the gun without any help from the “slide”. I guess I’m kind of confused on how the sear works as a disconnector by itself. Honestly I’m convinced that the sear is working as a disconnector in conjunction with the locking lever but I’m still not really sure how it’s working.

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    The heal of the sear interaction contact with the back of the trigger/shelf acts as the disconnector. The same design is used on HK 9X/MP5's, FN FAL, M1 Carbines to name a few.
    Bill
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    Why is it that you can get a binary trigger for mp5 clones and hk91 style rifles but they don’t have one for the Hk usc.

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