9mm on 80% lower

The #1 community for Gun Owners in Indiana

Member Benefits:

  • Fewer Ads!
  • Discuss all aspects of firearm ownership
  • Discuss anti-gun legislation
  • Buy, sell, and trade in the classified section
  • Chat with Local gun shops, ranges, trainers & other businesses
  • Discover free outdoor shooting areas
  • View up to date on firearm-related events
  • Share photos & video with other members
  • ...and so much more!
  • Wolffman

    Plinker
    Rating - 0%
    0   0   0
    Jul 19, 2012
    124
    18
    I finished an 80% lower, added the lower parts kit to finish it, and added a 9mm complete upper.
    When it fires, it is pretty decent. But, ~ 4-8 rounds out of a 31 round magazine will fail to cycle properly. That is, a round will fire, but then it will fail to completely eject the spent cartridge, and I usually have to pry the spent, mangled cartridge out of the action before I can have a new round insert into the chamber.
    It occurred to me that I didn't get a parts kit/stock meant for 9mm. It was probably meant for .223 or 5.56.
    Is it possible that my cycling problems are due to a spring that is too strong in the stock?
     

    d.kaufman

    Still Here
    Staff member
    Moderator
    Site Supporter
    Rating - 100%
    128   0   0
    Mar 9, 2013
    14,716
    149
    Hobart
    Im not 100% certain(dont have a 9mm ar) but i believe you need to run a heavy buffer for the 9mm. I know they make specific buffers for 9mm but i believe a H3 buffer is similar.
    Im sure someone that knows way more will be along shortly.
     

    gmcttr

    Grandmaster
    Site Supporter
    Rating - 100%
    12   0   0
    May 22, 2013
    8,593
    149
    Columbus
    A 9mm buffer is not only heavier than a carbine buffer but also longer to limit rearward travel. It is frequently used with a stronger spring (extra power or .308) to retard the rearward travel of a blowback 9mm bolt.
     

    JeepHammer

    SHOOTER
    Rating - 0%
    0   0   0
    Aug 2, 2018
    1,904
    83
    SW Indiana
    Besides buffer & spring, it could well be a mag misalignment issue, or extractor/ejector issue.
    With the case not being ejected it could be the extractor isn't holding the case long enough to solidly contact the ejector, or the ejector isn't doing its job.
    The spring/buffer you need to do anyway, then I would look into the extractor/ejector.
     

    G19G26

    Marksman
    Rating - 100%
    2   0   0
    Apr 5, 2008
    172
    28
    If you stay with a standard length buffer, you need to add either a spacer or 6 quarters to back of buffer tube. I run the quarters and heavy buffer with standard carbine spring.
    Good luck
     
    Top Bottom