Page 1 of 4 123 ... LastLast
Results 1 to 10 of 34

Thread: Diagnosis check...bolt speed?

  1. #1
    Join Date
    Mar 2010
    Location
    Braselton, GA
    Posts
    1,727
    Feedback Score
    26 (100%)

    Diagnosis check...bolt speed?

    So a guy and his son bring their newly-assembled AR out of the range because it's not running. The weapon consists of a PSA 16" M4 style upper on a gunshow special lower. I field stripped it and checked the carrier gey and gas tube...all good. I went into the range and watched them fire it and observed a failure to feed where the bolt partially closed on a live round but did not chamber it. Also, 3 or 4 instances of the following sequence:
    Insert loaded mag and chamber a round
    Pull the trigger and fire after which the bolt cycles, the spent case ejects, and the next trigger pull is "click" on an empty chamber.

    Carbine spring (good length) and carbine buffer.

    I gave them an H buffer to try and it helped marginally...basically it began crushing cases as mentioned above.

    My diagnosis is that the barrel is massively overgassed and I recommended they purchase an H3 buffer.

    Thoughts?
    Semper Paratus Certified AR15 Armorer

  2. #2
    Join Date
    Apr 2007
    Location
    FL
    Posts
    9,246
    Feedback Score
    28 (100%)

    Re: Diagnosis check...bolt speed?

    Is it consistently locking to the rear on an empty magazine?

    Typos brought to you via Tapatalk and autocorrect.
    Jack Leuba
    Director, Military and Government Sales
    Knight's Armament Company
    jleuba@knightarmco.com

  3. #3
    Join Date
    Mar 2010
    Location
    Braselton, GA
    Posts
    1,727
    Feedback Score
    26 (100%)
    Quote Originally Posted by Failure2Stop View Post
    Is it consistently locking to the rear on an empty magazine?

    Typos brought to you via Tapatalk and autocorrect.
    Yes, and I forgot to say I tried multiple mags that should have been good...Troy and USGI Magpul follower.
    Semper Paratus Certified AR15 Armorer

  4. #4
    Join Date
    Jan 2013
    Posts
    90
    Feedback Score
    1 (100%)

    Re: Diagnosis check...bolt speed?

    Where are the casings ejecting? 12 o'clock being the muzzle and 6 o'clock being the stock?

  5. #5
    Join Date
    Oct 2009
    Posts
    1,438
    Feedback Score
    12 (100%)
    PSA + Gun Show = Junk

    Why do you want to stamp your name on a woodshed build? I hope your getting paid handsomely...

    Quote Originally Posted by TactTeam View Post
    Where are the casings ejecting? 12 o'clock being the muzzle and 6 o'clock being the stock?
    Completely irrelevant...
    Last edited by MarkG; 08-17-13 at 14:37.

  6. #6
    Join Date
    Jan 2008
    Location
    AZ-Waging jihad against crappy AR's.
    Posts
    24,902
    Feedback Score
    104 (100%)
    Someone here pulled the FSB on a PSA carbine and it was around .093. My buddy locally grabbed a PSA upper out of curiosity and it was so overgassed it would run with an H3.



    Owner/Instructor at Semper Paratus Arms

    Facebook: https://www.facebook.com/SemperParatusArms/

    Semper Paratus Arms AR15 Armorer Course http://www.semperparatusarms.com/cou...-registration/

    M4C Misc. Training and Course Announcements- http://www.m4carbine.net/forumdisplay.php?f=141

    Master Armorer/R&D at SIONICS Weapon Systems- http://sionicsweaponsystems.com

  7. #7
    Join Date
    Oct 2010
    Posts
    962
    Feedback Score
    21 (100%)
    Was the bolt partially closed on the round like a bolt over base malfunction?



    Bolt over base malfunctions can be attributed to bad magazines but you ruled that out. I think they can also happen by short-stroking. In extreme cases I believe over-gassing can cause the bolt to outrun the magazine because of the carrier/buffer bouncing off of the inside of the receiver extension - This would also explain why the bolt returned without picking up the next round those 3 or 4 times.

    FWIW My BCM 16" middy will run anything with an H3 buffer. It does have over 5k through it though.
    Last edited by Eric D.; 08-17-13 at 17:18.
    B.A.S. Mechanical Engineering Technology

  8. #8
    Join Date
    Oct 2009
    Posts
    1,438
    Feedback Score
    12 (100%)
    Quote Originally Posted by Eric D. View Post
    In extreme cases I believe over-gassing can cause the bolt to outrun the magazine because of the carrier/buffer bouncing off of the inside of the receiver extension - This would also explain why the bolt returned without picking up the next round those 3 or 4 times.
    Given a serviceable magazine, the bolt group can't outrun it, period. This is one of those nagging errornet theories that just won't die.

  9. #9
    Join Date
    Mar 2010
    Location
    Braselton, GA
    Posts
    1,727
    Feedback Score
    26 (100%)
    Quote Originally Posted by MK18Pilot View Post
    Given a serviceable magazine, the bolt group can't outrun it, period. This is one of those nagging errornet theories that just won't die.
    Really? How is that impossible?

    I suppose another option is that the lower is out of spec such that the mag catch is machined too low or something.
    Semper Paratus Certified AR15 Armorer

  10. #10
    Join Date
    Feb 2010
    Location
    FL
    Posts
    2,081
    Feedback Score
    5 (86%)
    Did you say what ammo they were using?

Page 1 of 4 123 ... LastLast

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •