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9mm ar-15 lower with 5.56 ar-15 upper?

Discussion in 'Rifle Discussion' started by aquariumjunky, Dec 7, 2009.

  1. aquariumjunky

    aquariumjunky Albany, Oregon Active Member

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    So title basically says it all will it be smooth like butter or would it cause all kinds of trouble?

    Probally a RRA 9mm hammer and a 8.5 ounce 9mm buffer

    Let me know what you think?

    Steven
     
  2. cyclesarge

    cyclesarge Eugene OR, DUH! We're ALL in the NORTHWEST Well-Known Member

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    So you are asking if you can run a standard AR Upper with a 9mm barrel and bolt and have it run smoothly? I asked the same question on another forum and got the answer that it would work. You will have an extra hole up front for the non-existent gas tube, no brass deflector, larger than necessary ejection port, and a non-functioning forward assist. I went ahead and bought a 9mm upper not too much extra money ($35 extra) and no extra holes.:thumbup:
     
  3. NoAim

    NoAim Hillsboro, OR Active Member

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    I don't know about the whole 9mm hammer situation. Some say good, some say bad, either way...I don't know.

    With that heavy of a buffer, you'll likely be short stroking unless it's suppressed. So, grab a regular carbine or H buffer for use with the 5.56.
     
  4. aquariumjunky

    aquariumjunky Albany, Oregon Active Member

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    Let me clear it up a bit. a complete standard 5.56 upper nothing to do with 9mm at all on a standard lower but with a 9mm hammer and heavy buffer.

    Sounds like a second buffer which is really cake to swap out would be needed but what about using the 9mm hammer on the 5.56 upper?

    Steven
     
  5. cyclesarge

    cyclesarge Eugene OR, DUH! We're ALL in the NORTHWEST Well-Known Member

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    I don't think the 9mm hammer will work. I have a regular AR hammer that works with both my 5.56 upper and my 9mm uppers. I also use a 4.3 oz buffer for both, I just add buffer spacer for the 9mm. Make sure you don't have an extended buffer , if you are going to use it with 5.56. If it's 8.5 oz it's probably extended.
     
  6. zul

    zul PDX Member

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    Something tells me a 9mm round will not be fitting through the 5.56 barrel ;)
     
  7. aquariumjunky

    aquariumjunky Albany, Oregon Active Member

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    Ok I am a little fuzzy on my geometry So a 9mm projectile won't fit down a 5.56mm hole?

    Now I am confused?

    How about can I shoot 5.56 through a 5.56 upper when it is mated to a 9mm customized stripped lower with the 9mm magblock removed?

    Steven
     
  8. cyclesarge

    cyclesarge Eugene OR, DUH! We're ALL in the NORTHWEST Well-Known Member

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    Other than the magblock and the hammer, is there anything that is different between your "customized stripped lower" and an ordinary AR lower?
     
  9. aquariumjunky

    aquariumjunky Albany, Oregon Active Member

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    Heavy extended buffer but that already sounds like a no go so I will keep another buffer handy incase I want to shoot 5.56. Mostly now I am tring to find out if the RRA 9mm hammer will work with a 5.56 upper? to shoot 5.56 so there is no confusion.

    Steven
     
  10. krawl

    krawl Oregon Member

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    Shouldn't be a problem. I ran my, now stolen, 11.5" upper on my lower with a 9mm hammer and buffer. Ran no problems.
     
  11. bnr32gtr

    bnr32gtr Vancouver, WA Member

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    I run a MEGA lower with an RRA 9mm buffer, 9mm spring and DPMS hammer and can swap out and run my 5.56 MEGA upper on it with ZERO trouble. Smooth as can be and a doll to shoot.

    About two months ago I let a couple friends try out the 9mm buffer and recoil spring in their 5.56 uppers and when they got home, they both ordered a set for themselves!

    I used to run a 9mm hammer but with the harder Barnaul/Brown Bear .223 primers I would get a failure to fire. Switched to the DPMS hammer as it works with every caliber I have: .22lr, 9mm, 5.56 and 7.62x39.