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Feed Problems

Discussion in 'Maintenance & Gunsmithing' started by jdtaylor45, Sep 8, 2015.

  1. jdtaylor45

    jdtaylor45 Beaverton, OR New Member

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    Hey, I built a new AR15 from parts kit. I got the kit and parts from different places. I put it together and it all seems to work correctly. But when I try it with live ammo, it malfunctions. It seems that when the bolt comes forward and strips off a round from the magazine, the bold turns very slightly as it does this. When it slams shut, the splines of the bolt don't mesh with the slots in the barrel. What causes this? I've polished the feed ramp, I've tried new and different magazines, I've dried different bolts and even whole bolt assemblies and it is always the same... any ideas?
    Ar trouble.jpg

    Ar trouble.jpg
     
  2. zeppelin

    zeppelin Benton County WA Active Member

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    Best guess is barrel not headspaced properly. The barrel/chamber has to be screwed in just the right amount in order for the cartridge headspace to be within spec. If this wasn't done correctly it could affect the position of the chamber grooves that mate with the the protrusions on the rotating bolt head. How did you adjust the headspace on this firearm when you built it?
     
  3. zeppelin

    zeppelin Benton County WA Active Member

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    Trying to research this a bit suggests headspacing is normally a fairly complicated exercise with the AR 15 and is normally done by manufacturers (involves some milling). If you buy your bolt and barrel from the same place they will usually make sure the two are properly headspaced. I surmise if you go with different manufacturers for these critical parts, you could end up with improper headspace.
     
  4. Uberdillo

    Uberdillo Oregon Active Member

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    If we're just taking WAGs, I'd find a set of GO/NO-GO gauges, whether borrowing from someone on here or checking in at your local LGS or gunsmith and check that for good measure. If ok, try some different ammo, if not, time to send it back assuming you weren't the one to headspace the extension to the barrel.
     
  5. Velzey

    Velzey Estacada, Oregon Gunsmith Gunsmith Bronze Vendor Bronze Supporter

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    Your bbl extension does have the pin in it? And are the lugs on your bolt well lubed? New builds sometimes need to be worked a little with grease or lapping compound. Or did you buy a barrel that is actually short chambered and it needs to be finished reamed...
    barrel ex.jpg

    barrel ex.jpg
     
  6. Certaindeaf

    Certaindeaf SE Portland Well-Known Member

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    Hey, I've never screwed one a those together but "headspace" proper is disparate from how the "lugs" wind up being.. or want to wind up being, meaning the both are connected, especially upon (hopefully) "functioning".. anyway good luck
     
  7. blackadder

    blackadder Everett Bronze Supporter Bronze Supporter

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    I had a similar issue. The problem turned out to be that the slot to receive the barrel nipple was too wide and the barrel canted in the slot. Could be that your barrel is canted to one side.
     
  8. ZA_Survivalist

    ZA_Survivalist Oregon AK's all day.

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    Sounds silly but.. Is the bolt face backwards?
     
    rick benjamin likes this.
  9. ZA_Survivalist

    ZA_Survivalist Oregon AK's all day.

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    My eyes ain't too güd.
     
  10. blackadder

    blackadder Everett Bronze Supporter Bronze Supporter

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    Can't complain too much when I paid $30 for the upper receiver [emoji2]