How to get maximum delay on MP5 action
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Thread: How to get maximum delay on MP5 action

  1. #1
    LHH
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    Default How to get maximum delay on MP5 action

    I found some related questions and posts, but not a direct answer. I am working on a project with subsonic ammo and long barrel.
    I need to keep the bolt closed as long as possible before opening.
    Cycle time, dwell time or rate of fire do no matter, only keeping the bolt closed as long as possible.
    My guess is the three variables are:
    Locking piece angle
    Recoil spring
    Weight of bolt


    Does a known combination exist to keep action locked as long as possible(and still reliably cycle)?
    Remember, cycle, dwell or rate of fire time does not matter.

    Thanks in advance

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    What is the application, what are you hoping to accomplish by doing this? Are you just trying to decrease wear?

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    I would focus first on the locking piece, since the angle of the shoulders dictate the length of time the the rollers remain engaged before the bolt begins rear-ward travel. Keeping the rollers engaged and the bolt in place longer might necessitate a weaker recoil spring, rather than a stronger spring. Coupled with a heavier bolt (how much tho?) you are probably going down the right track.

    Are you planning to run this rig with a suppressor, which will increase back pressure?
    Last edited by Spitfyr; 05-24-2020 at 08:18 PM.

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  5. #4
    LHH
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    I am trying to ensure the action does not cycle or moves a little as possible until the bullet has left the barrel.
    In the AR world, using 223 standard ammo bullet is only a few feet from the barrel when it cycles, something like 1.3 milliseconds according to Springfield armory tech docs. A subsonic bullet may take 2.5 milliseconds to exit a long barrel using Quickload.
    On paper, the slow bullet is still in the barrel when cycling is going on.
    Probably never be sure either way, but slowest possible action unlock is best insurance in this case.
    If someone can recommened a good HK gunsmith that would helpful as well.

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    Quote Originally Posted by LHH View Post
    I am trying to ensure the action does not cycle or moves a little as possible until the bullet has left the barrel.
    In the AR world, using 223 standard ammo bullet is only a few feet from the barrel when it cycles, something like 1.3 milliseconds according to Springfield armory tech docs. A subsonic bullet may take 2.5 milliseconds to exit a long barrel using Quickload.
    On paper, the slow bullet is still in the barrel when cycling is going on.
    Probably never be sure either way, but slowest possible action unlock is best insurance in this case.
    If someone can recommened a good HK gunsmith that would helpful as well.
    So you're trying to reduce sound first and foremost, which is why you're shooting a slow bullet but you want it to leave the barrel as fast as possible?

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    Edit:i'm retarded

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    That is not a correct use of words in todays society of snow flakes... you should have said HK challenged.
    Quote Originally Posted by A_Blind_Man View Post
    Edit:i'm retarded

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    Just a note, the MP5 SD barrel has ports drilled on the proximal side to the chamber to drop a standard factor load 9mmx19 round to below 1000 fps.

    This reduces the firing rate from 13 to 11 rps.

    You may end up just having to copy the MP5 SD design

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    LHH
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    Keeping it quiet keeps the peace with neighbors and saves trips to the range.
    Picked up an SL6 and MP5 clone by chance, so new to these kinds of actions.

    Can control speed as I reload, so no issue there.
    Not using a suppressor.


    Thanks for the tip about the MP5 SD, will look into it.
    Last edited by LHH; 05-25-2020 at 02:10 AM.

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    Quote Originally Posted by LHH View Post
    Keeping it quiet keeps the peace with neighbors and saves trips to the range.
    Picked up an SL6 and MP5 clone by chance, so new to these kinds of actions.

    Can control speed as I reload, so no issue there.
    Not using a suppressor.


    Thanks for the tip about the MP5 SD, will look into it.
    I'm confused why you are not planning on using a suppressor with subsonic ammo, which will give you very quiet performance. If you want to keep the neighbors happy subsonic ammo will still produce a significant muzzle 'boom' without a suppressor but eliminates the supersonic crack downrange...not a very good trade off in my book. Given the choice I'd run the suppressor and subs. When I do this shooting at steel without earmuffs, the report of the rounds hitting the steel is incredibly loud compared to the gun.

    https://www.youtube.com/watch?v=1PfOs8VPpSA

    edit: maybe you live in a state that does not allow for suppressors?
    Last edited by Spitfyr; 05-25-2020 at 06:18 AM.

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