Ar15 build help

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!
  • Rookie

    Grandmaster
    Rating - 100%
    14   0   0
    Sep 22, 2008
    18,155
    113
    Kokomo
    San Tan upper and Faxon barrel.
    705963239.jpg

    Changing the bolt carrier group doesn't fix it. With no bolt in, the upper opens and closes with ease. Install the bolt, and you have to slam it to get it to open and close. Thoughts? Suggestions?
     

    Mgderf

    Grandmaster
    Site Supporter
    Rating - 100%
    43   0   0
    May 30, 2009
    17,879
    113
    Lafayette
    Evidently the bolt carrier is not moving forward enough.
    Have you cleaned/lubed the bolt/carrier?
    A very stiff, or dry, bolt might cause this issue.
    Good luck
     

    Rookie

    Grandmaster
    Rating - 100%
    14   0   0
    Sep 22, 2008
    18,155
    113
    Kokomo
    Removing the bolt face from the bolt carrier group does not solve the issue. The bolt still doesn't sit flush on the back end of the upper...
     

    dieselrealtor

    Master
    Rating - 100%
    177   0   0
    Nov 5, 2010
    3,271
    77
    Morgan County
    if changing the BCG doesn't change anything, the only other thing I can think of is upper out of spec. Can you see any marks inside the upper where the bcg is hanging up?

    FA not in the way or hanging up?
     

    Rookie

    Grandmaster
    Rating - 100%
    14   0   0
    Sep 22, 2008
    18,155
    113
    Kokomo
    No marks. Slamming the forward assist doesn't budge the bcg. It looks like it's as tight as it can go. I'm leaning towards either barrel or upper is out of spec, but I have no idea how to figure that out.
     

    dieselrealtor

    Master
    Rating - 100%
    177   0   0
    Nov 5, 2010
    3,271
    77
    Morgan County
    with the bolt removed, you could cover the end of the bcg or barrel with tape, install the BCG & see if the tape is crushed. I would think that would validate or invalidate the barrel being out of spec.

    Or if you have a caliper with long enough rod you could check depth from the back of the upper to the barrel & compare against a known good one.
     

    NyleRN

    Master
    Rating - 100%
    28   0   0
    Dec 14, 2013
    3,834
    113
    Scottsburg
    Try a different carrier. If that doesn't work, try a different gas tube. You can put the carrier in and turn the upper upside down and watch it slide from underneath. Watch and see how well the gas tube enters the key
     

    bgarman47

    File Jockey
    Rating - 100%
    4   0   0
    Feb 8, 2023
    153
    43
    Ossian
    If you have a good set of calipers, measure the OAL of the carrier. It should be no more than 6.875".

    Remove the bolt and drop the carrier into the receiver. You shouldn't feel the carrier key interact with the gas tube on the way forward. If the gas tube is binding in the key this can cause your issue as others have mentioned. Could be a bent or improperly attached key. I've actually seen more of this on cheaper BCGs than I've seen bent gas tubes.

    ETA: this could also be caused by the hole for the gas tube to pass through the upper being off location. If the gas tube is binding, try checking that out by inserting a pin gauge (or the smooth side of a tightly fitting drill bit) into the carrier key and check alignment by inserting the carrier into the upper slowly.
     
    Last edited:

    gassprint1

    Expert
    Rating - 100%
    4   0   0
    Dec 15, 2015
    1,074
    113
    NWI
    Any results with whats suggested? Have you tried removing the charge handle and just insurting the bcg? Or try another bcg?
     

    tinmansinoz

    Plinker
    Site Supporter
    Rating - 100%
    1   0   0
    Feb 27, 2023
    26
    3
    Brownsburg, IN
    Oh man...I don't want to hurt any feels but are you married to SanTan? Perhaps get that money back? I'm no expert and I know there's countless manufacturers out there but dang man. We should all be able to build a frankengun without concerns like these. Either way, glad you found the problem, good luck on the replacement.
     

    31ST MEUSOC

    Shooter
    Rating - 0%
    0   0   0
    Oct 27, 2023
    39
    18
    PA
    Do you have chamber guages check your go and no go guages to see what happens but before you do it seriously clean it first.
     
    Top Bottom