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9mm AR-15

PapaBSRPapaBSR Member Posts: 25 ✭✭
edited June 2015 in Ask the Experts
I have a JSE upper with the CMMG BCG. I have a New Frontier Polymer Lower. The buffer has been replaced by a CMMG 9mm buffer. The hammer is clearing the bolt. When I charge the carbine using the charging handle the hammer cocks. When the carbine is fired it expels the spent round and chambers a new round. However the hammer is not staying cocked. Why? If I pull the bolt even half way open the hammer cocks. But during the cycling of the carbine when firing it. The hammer does not stay cocked.

Comments

  • rufe-snowrufe-snow Member Posts: 18,649 ✭✭✭
    edited November -1
    I have never owned a 9mm AR conversion. I believe it is blowback rather than gas operated. Like the conventional .223/5.56 AR's. You might try hotter loaded 9mm ammo. Lot of the U.S. stuff, is loaded to be lawyer proof.

    I was just reading the latest issue of the "American Rifleman". They were cronoing 115 & 124 grain loads out of a handgun. They were reading at just over 1000 FPS muzzle velocity. I believe these loads should be 100 FPS higher FPS wise, for positive function.
  • mark christianmark christian Forums Admins, Member, Moderator Posts: 24,511 ******
    edited November -1
    You need a dedicated 9mm hammer or you have to ramp the bolt carrier to allow it to function with the .223 hammer, which will cock fine using the charging handle but it won't cock during the firing cycle due to the notches not being compatible.

    I'm not a gun smith, and liability issues resulting from handing out advice on fire control modifications means I recommend getting the 9mm hammer.
  • v35v35 Member Posts: 13,200
    edited November -1
    You have a disconnector or disconnector spring problem.
    Remove the upper and cock the hammer while holding the trigger back.
    If the hammer doesn't stay back or barely hangs on, you need disconnector work, meaning that forward leg of the disconnector that bears on the sear needs to be ground away sufficiently for the disconnector to engage the hammer with the trigger fully rearward.
  • fordsixfordsix Member Posts: 8,722
    edited November -1
    does it still have the plastic hammer,,the CMMG bolt works with standard AR 15 hammers
  • PapaBSRPapaBSR Member Posts: 25 ✭✭
    edited November -1
    Well folks.
    The standard hammer does not work with the NFA's trigger. The statement for the NFA's blowback hammer states "Some blowback uppers (including JSE 9MM uppers) may require additional fitting on the hammer to clear the carrier." The CMMG BCG claims you can use it on any standard lower. Not the ******* NFA lower. So much for the idea of interchangeable parts. The New Frontier lower and the JSE upper might just be a marriage made in hell. I bought the NFA lower because it was inexpensive and I was just making up a fun gun. But if I end up having to replace the hammer/trigger group. I could have just bought an Andersen lower for the same price by the time I get done making this cheap piece of plastic to work. I guess if it looks like a black gun on the outside it should sell.
  • fordsixfordsix Member Posts: 8,722
    edited November -1
    get rid of the NFA lower and get a real lower[;)]
  • PapaBSRPapaBSR Member Posts: 25 ✭✭
    edited November -1
    I replaced the entire fire control group with metal parts and she is functioning properly. It was a forty five dollar lesson. But as least I have a functioning toy rather then just a display item. Thank you for your responses.
  • fordsixfordsix Member Posts: 8,722
    edited November -1
    like it now! put on a slidefire..mag dump in 1.1 sec
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