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Mossberg loose stock screw

Discussion in 'Maintenance & Gunsmithing' started by CleverName, Nov 19, 2011.

  1. CleverName

    CleverName Southern Oregon Active Member

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    Hello. I have a Mossberg 590A1 with a 12" LOP Hogue stock. The stock screw has come loose on me twice, even with blue Loctite. This last time, I degreased the receiver and screw and used blue Loctite again (Im hesitant to use red loctite on an aluminum receiver) . I also used a lock washer and I scuffed up the standard washer under the lock washer to give it some bite. I noticed the screw only threads into the reciever about halfway. If it comes loose again Im going to use a longer screw.
    Other than that does anyone have any tricks for keeping a stock screw tight?
     
  2. RVTECH

    RVTECH LaPine Well-Known Member

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    Seems odd the screw coming loose (and twice) but you might consider making a long 'stud' (TBE) and use blue locktite to secure it in the receiver end and then with threads on the other end use locktite and a nylock nut to secure the stock. Otherwise continued loosening of the screw is going to wear out the threads in the receiver (which may already be part of the problem) and you may eventually have to go oversize on the screw.
     
  3. Bigbaddude

    Bigbaddude West linn Oregon Bronze Supporter Bronze Supporter

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    Locktite goes bad. I think once open it only last for 6 month maybe a year.
     
  4. CleverName

    CleverName Southern Oregon Active Member

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    I didnt know this. Its a fairly old tube of loctite Im using. Perhaps this is the issue? And that stud w/ nylon nut is also a pretty good idea. If it comes loose again I'm going to use a fresh tube of Loctite and a longer screw.
     
  5. rpatton

    rpatton Graham WA Member

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    Has the stock been replaced perhaps by a previous owner? Of course this idea is out if you are the original owner but the first question that came to mind was "Is it the right screw?"
     
  6. CleverName

    CleverName Southern Oregon Active Member

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    I bought the shotgun new, and replaced the stock with a Hogue short LOP stock. Im using the original stock screw. The screw protrudes from both the original stock and Hogue equally. It should be a little longer though. There's some unused threads in the receiver. If it loosens again I'm going to use a longer bolt.
     
  7. mattg521

    mattg521 portland.,or Member

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    How many threads are you currently engaging? How many more avail?
     
  8. civilian75

    civilian75 Hillsboro, OR Well-Known Member

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    If screw i short, i'd try to replace it with a longer screw asap. If not, you may risk stripping the screw and worst yet, the nut soldered to the receiver. You could be placing too much stress to too little thread surface as it is.
     
  9. CleverName

    CleverName Southern Oregon Active Member

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    The rear wall of the receiver is a little over 1/2" thick. I would say the screw is through a little over half that. Without pulling the screw out again, I would estimate its engaging about six threads with four threads still available.
     
  10. jbett98

    jbett98 NW Oregon Bronze Supporter Bronze Supporter

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    Notes on nuts. (found this article online)


    As nuts and bolts are not perfectly rigid, but stretch slightly under load, the distribution of stress on the threads is not uniform. In fact, on a theoretically infinitely long bolt, the first thread takes a third of the load, the first three threads take three-quarters of the load, and the first six threads take essentially the whole load. Beyond the first six threads, the remaining threads are under essentially no load at all. Therefore, a nut or bolt with six threads acts very much like an infinitely long nut or bolt (and it's a lot cheaper).

    Stress on threads

    Stress on bolt threads. Note how the majority of
    the stress is on the first thread to the left.
    Image from Spiralock.



    Thread % % Sum
    1 34% 34%
    2 23% 55%
    3 16% 71%
    4 11% 82%
    5 9% 91%
    6 7% 98%

    There is little point in having more than six threads in anything. Nuts with National Coarse threads typically have 5 threads in them, whereas nuts with National Fine threads have about 8 threads. Nuts are usually stronger than the bolts they are on, which is to say that the bolt will usually break before the nut strips.

    It is often said that two threads must be exposed above a nut. The reason for this is that the first two threads of a bolt are often poorly formed, and may not engage the nut properly. If they're not doing their share, the other threads in the nut will be overloaded, and the nut may strip.
     
  11. CleverName

    CleverName Southern Oregon Active Member

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    This is good info. Thank you.