BCG fits to snug in upper reciever

Discussion in 'Gunsmithing Forum' started by matt82527, Dec 3, 2013.

  1. matt82527

    matt82527 New Member

    2
    0
    0
    Currently building an ar-15 SBR (legally w/tax stamp). Anyways upon assembly I noticed the BCG fits very snug in the upper receiver. I can push it all the way in until the lugs lockup in the chamber. But it will not slide freely like it does in my other ar's. So my question is more or less can I take some sort of abrasive and polish down the lower edges of the bcg (which is where I believe it is catching) or should I fully complete the rifle, lube it up good and just work the action (chamber empty) to break it in a little. I have never had this happen in my other ar builds, so this is a new one on me.
     
  2. JonM

    JonM Moderator

    20,110
    19
    38
    take the bolt out of the carrier and run just the carrier in the upper. if its not binding your just experience the gas rings doing their job.

    just shooting it should wear it in over time long as its not like having to be pried out of the upper.
     

  3. SSGN_Doc

    SSGN_Doc Well-Known Member

    6,926
    61
    48
    If the carrier is dragging excessively without the bolt installed then something is out of spec.
    If you have calipers you can measure the inside diameter of the receiver against one if your existing uppers. And BCG against an existing one or just try swapping parts around and see which part doesn't fit properly.
     
  4. Sgt_Skrb_25

    Sgt_Skrb_25 New Member

    1,983
    0
    0
    Another thing to consider is the gas tube and gas key. I just had an issue with a finished rifle. It was a RRA upper receiver, DPMS gas tube and a FailZero BCG. It was doing the same thing. What happened was the NIB coating was to thick in the gas key causing the inner diameter to be too tight. I checked it with 4 other BCG's and it worked fine. I swapped out bolts and carriers. It would lock forward but difficult to charge back. When using the other carriers it was fine. I had to polish out the inside if the gas key and now it has no resistance. At first I thought it was the swedge at the end I the gas tube, but other carries would fit just fine. Just another thing to look at.
     
  5. gunnut07

    gunnut07 New Member

    944
    0
    0
    I would get some layout fluid and put it on the bolt carrier and run it back and forth a few times in the upper. Just to see if one part is rubbing more than another. Might just need some lapping in, I have seen that happen.

    http://www.zorotools.com/g/00063640/k-G0599182?utm_source=google_shopping&utm_medium=cpc&utm_campaign=Google_Shopping_Feed&kw={keyword}&gclid=CNOUiMr7lrsCFSLxOgod9zQAFg
     
  6. purehavoc

    purehavoc New Member

    4,799
    2
    0
    I put a upper together for a guy and my gas tube alignment tool got stuck in his upper , enough that I actually broke the pull handle on the tool , never had this happen on any other upper , Im guessing it was out of spec a bit . you may be experiencing the same thing
     
  7. matt82527

    matt82527 New Member

    2
    0
    0
    Ok. Thanks for your help guys. I failed to mention that the bolt carrier has some sort of coating on it, and that may be the reason why it I hanging. That coating may be just thick enough to throw it out if spec. I will put some calipers on it and the upper and see what I come up with.