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Thread: SP5 as sear host?

  1. #31
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    "So if you were to mill away part of the trip lever engagement ramp on a MP5 full auto carrier enough to clear the carrier block in an SP5, it looks like you would be left with about ~50% of the sear trip ledge on the MP5 carrier in order to clear the block. Unfortunately that is also the critical area on the MP5 carrier where the sear trip lever in the pack hits the trip ramp on the carrier.

    However, if you were to thicken/widen the sear trip lever in the pack on the left side.... say by cutting the triangular portion off the end of a spare sear trip lever, and welding or soldering that cut piece of trip lever to the left side of the existing sear trip lever in the pack (essentially doubling the sear trip lever area thickness on the left side), it looks like there may be enough of the trip ramp left on a MP5 full auto carrier to engage a modded/thickened sear trip lever, even after removing part of the sear trip ledge on the carrier to allow it to clear the carrier block in the receiver "

    Yes.
    I mean I dont know if it will work yet, possibly. But I do know this is the path, if you cut the nubbin off the reciever, machine gun.
    Unfortunately this is it, no mods to the receiver, period, or machine gun.

  2. #32
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    Back of the bolt may catch when rollers in and...bad news. It late.

  3. #33
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    All said I would still prefer a 94 for host.
    Last edited by ottomatik; 12-07-2019 at 05:34 AM.

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  5. #34
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    I agree I would still prefer a 94 as a sear host all things considered.

    However if you look at the bottom of the MP5 bolt the cut on the bolt is just as wide as the sear trip lever slot on the carrier. So as long as a modified trip fit through the the relief slot carrier forward of the trip ramp you would be fine on the bolt as well as the relief slot on the underside of the bolt is identical in width.

    In the attached pic you can see the mark in the oil/grease where the trip is currently hitting the trip ramp on the carrier and the marked area in red to the left (or top on the photo in the current orientation) that could be utilized to engage a modded lever that was either offset or thickened.

    The big question is can you remove the area below the red mark, (roughly where the trip is currently hitting and to the right), and still have it clear the carrier block in the SP5 receiver or does basically the entire trip area have to be removed to clear the block in the receiver.
    Attached Thumbnails Attached Thumbnails SP5 as sear host?-mp5_carrier_trip.jpg  
    Last edited by jbntex; 12-07-2019 at 05:55 AM.

  6. #35
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    Yes, looks possible, and you are on the right path, but I am still not sure about that corner on the backside of the bolt, might hang on modified lever. If it does, bad. Lots of mods to get it running, SP5 destined to be SBR only, as the fine folks at HK and ATF desire. In fact I bet next run of SP5k have same repositioning of nubbin to achieve same outcome. And these are the last, it seems our friends at Orbendorf are out of parts, what up with that rear sight, retooling for actual production will take serious time and money for an outdated platform. Honestly I am surprised that barrel made it through the gauntlet as well...perhaps additional reason to make it sear incompatible, just random thoughts late at night...
    Last edited by ottomatik; 12-07-2019 at 06:40 AM.

  7. #36
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    Quote Originally Posted by Nonflammable View Post
    Removing the block in an SP5 seems akin to drilling a 3rd pin hole in an AR lower.
    I think you are thinking about this the wrong way, drilling the 3rd hole in an AR lower holds the autosear, an absolutely required part for reliable F/A fire. The hole you drill on a HK roller lock that would be equivalent is the front push-pin hole. That would let you easily (assuming you have done the extensive metal work removing the semi shelf) attach an autosear inside an unmodified F/A pack.

    Removing the SP5 block is like removing the old Colt autosear blocks (that projected out of the top of the lower receiver) on AR rifles in the 80s. Both blocks require the use of a modified carrier (the infamous "C" carrier in the case of the Colt) that has material removed to avoid contact with an autosear (should one be present). We don't have sear blocks in ARs any more, and I don't think you need one for a HK gun...other than to appease ATF bureaucrats who get to use ATF policy (not exclusively the law) to determine what is importable into the US.

    Remember, guns just have to meet the standard of not being "easily convertible" they don't have to be impossible to illegally modify. That is why we now use standard carriers in our ARs, and many young shooters have (fortunatly) never seen an AR sear block or a C carrier. You can mill off a Colt sear block without a problem vis a vis the ATF, so removing blocks isn't necessarily seen as a step toward conversion in that case.

    Seeing the general acceptance of the sear block on the SP5, I wonder if we are going to see Colt-style sear blocks on new MR rifles coming into the U.S.?
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    Quote Originally Posted by jbntex View Post
    I agree I would still prefer a 94 as a sear host all things considered.

    However if you look at the bottom of the MP5 bolt the cut on the bolt is just as wide as the sear trip lever slot on the carrier. So as long as a modified trip fit through the the relief slot carrier forward of the trip ramp you would be fine on the bolt as well as the relief slot on the underside of the bolt is identical in width.

    In the attached pic you can see the mark in the oil/grease where the trip is currently hitting the trip ramp on the carrier and the marked area in red to the left (or top on the photo in the current orientation) that could be utilized to engage a modded lever that was either offset or thickened.

    The big question is can you remove the area below the red mark, (roughly where the trip is currently hitting and to the right), and still have it clear the carrier block in the SP5 receiver or does basically the entire trip area have to be removed to clear the block in the receiver.

    The carrier block is exactly in line where the trip lever would contact the carrier ramp, so I don't thing that would work, unfortunately. You almost need to have some sort of removable ramp that can be screwed in place on the carrier once it's inserted into the receiver.
    Last edited by LRM19k; 12-09-2019 at 12:26 PM.

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    Quote Originally Posted by LRM19k View Post
    The carrier block is exactly in line where the trip lever would contact the carrier ramp, so I don't thing that would work, unfortunately. You almost need to have some sort of removable ramp that can be screwed in place on the carrier once it's interested into the receiver.
    This was my first thought on how to defeat the block but probably not going to be easy for the avg Joe like me to machine.

    That would bring up another question... would a "screwed-in trip ramp" hit the block as the carrier recoiled? Anyone have an opinion on that...does the carrier travel that far back during recoil?

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    Quote Originally Posted by LRM19k View Post
    The carrier block is exactly in line where the trip lever would contact the carrier ramp, so I don't thing that would work, unfortunately. You almost need to have some sort of removable ramp that can be screwed in place on the carrier once it's interested into the receiver.
    Agreed, the current block appears to be right in line with where the full auto trip lever is. However, look at the attached pic you can see how little of the block actually appears to be in the way of the MP5 full auto carrie ramp. It looks like maybe as little as 25% of the full auto trip ramp on an MP5 carrier would need to be milled away so that a MP5 full auto carrier would fit past the block.

    That leaves you with what appears to be at least 50% of the ramp on the carrier left. At that point you just need a new updated trip lever with a slightly widened engagement surface to engage that remaining portion of the ramp on the MP5 full auto carrier.

    The angle of this picture isn't ideal, what we need to see is the same pic/mockup of a MP5 carrier being inserted into an SP5 but looking directly down into the receiver to see the exact overlap area on the MP5 carrier that has to be removed.
    Attached Thumbnails Attached Thumbnails SP5 as sear host?-sp5_sear_block.jpg  

  11. #40
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    LRM-I think you got it, but who is going to want to attach a removable after inserted? Way past desirable smithing for end result, get a clone or a 94. Probably better to leave the few of these that come in NIB and not go through all of the trouble for a "blaster", just my 2 cents.
    Enjoy the sunset and be thankful a few more made it in, to all that pick one up!

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