View Poll Results: Broken bolts related to gas sytem

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  • Carbine

    16 72.73%
  • Midlength

    3 13.64%
  • Intermediate

    0 0%
  • Rifle

    3 13.64%
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Thread: Has anyone experienced a broken bolt or sheared lug?

  1. #1
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    Has anyone experienced a broken bolt or sheared lug?

    What gas system were you using?
    Quote Originally Posted by Jaykayyy
    And to the guys whining about spending more on training, and relying less on the hardware, you just sound like your [sic] trying to make yourself feel superior.

  2. #2
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    Someone 2 places down the firing line from me sheared a lug one day. Standard M4A1. As issued (carbine length gas system). M855A1 ammo. Lug that sheared was adjacent to the extractor. For what it is worth, the RO stated he has seen more sheared lugs since the introduction of M855A1.

  3. #3
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    Seen a few on M4a1’s. With regular green tip. Usually discovered when cleaning.

    Edit: lugs.
    Last edited by 1168; 03-28-20 at 19:35.

  4. #4
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    Yes, but both times the bolt was defective to begin with. All of my Colt or BCM bolts lasted the life of the barrel no matter the gas system. Lesson: buy a quality bolt.

  5. #5
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    Broke the bolt on a student M4A1 at Fort Bragg at a shooting course. Bolt sheared at the cam pin hole.

    That carbine had so many rounds through it the bird cage had extreme flame-cutting on the down-range side of each of the compensator slots.

  6. #6
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    I saw a few bolts break on M16s and M4s while I was an XO for a basic training company. Healthy diet of M855 green tip ammo, and the rifles were abused by the privates. I remember one sheared lug jammed up a gun during rifle zeroing. With the consistent rounds these guns received along with lack of maintenance, I'm not surprised.

    I was cleaning my wife's BCM rifle last night (14.5 mid length) and saw one of the bolt lugs was chipped. Put in an order for a new one and will be swapping it out.

    IMG_20200327_221318.jpg
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  7. #7
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    Gas system length is one of many factors that contribute to a broken lug

    These factors would include:
    Round count
    Bolt coating
    Coating method and post-treatments
    Gas system length
    Ammo
    Gas port size
    Dimensions
    Heat treatment (was it done properly?)
    Shot peening
    Base metal chemistry
    Inclusions
    Rate of fire

    *a lot of these interact and Im sure Im missing some, this is just off the top of my head.

    If someone had a sheared lug, and what gas system is, by itself, worthless info IMO.
    Last edited by MegademiC; 03-28-20 at 18:33.

  8. #8
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    Quote Originally Posted by MegademiC View Post
    Gas system length is one of many factors that contribute to a broken lug

    These factors would include:
    Round count
    Bolt coating
    Coating method and post-treatments
    Gas system length
    Ammo
    Gas port size
    Dimensions
    Heat treatment (was it done properly?)
    Shot peening
    Base metal chemistry
    Inclusions
    Rate of fire

    *a lot of these interact and Im sure Im missing some, this is just off the top of my head.

    If someone had a sheared lug, and what gas system is, by itself, worthless info IMO.
    I understand that this isn't scientific. I'm just trying to get a general picture whether or not people are/were/have experienced some of the common issues attributed to the violence of the carbine gas system in other gas systems. Or if some of the advances (LMT enhanced BCG, KAC E3) are rendered mostly moot if you're no longer running a carbine gas system.
    Last edited by Sry0fcr; 03-30-20 at 10:24. Reason: clarity
    Quote Originally Posted by Jaykayyy
    And to the guys whining about spending more on training, and relying less on the hardware, you just sound like your [sic] trying to make yourself feel superior.

  9. #9
    Join Date
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    Quote Originally Posted by MegademiC View Post
    Gas system length is one of many factors that contribute to a broken lug

    These factors would include:
    Round count
    Bolt coating
    Coating method and post-treatments
    Gas system length
    Ammo
    Gas port size
    Dimensions
    Heat treatment (was it done properly?)
    Shot peening
    Base metal chemistry
    Inclusions
    Rate of fire

    *a lot of these interact and Im sure Im missing some, this is just off the top of my head.

    If someone had a sheared lug, and what gas system is, by itself, worthless info IMO.
    You forgot firing a proof round, according to Knight's that cuts the bolt life in half, KAC skips that and warranties their bolts for 22,000 rounds.
    “The Trump Doctrine is ‘We’re America, Bitch.’ That’s the Trump Doctrine.”

    "He is free to evade reality, he is free to unfocus his mind and stumble blindly down any road he pleases, but not free to avoid the abyss he refuses to see."

  10. #10
    Join Date
    Jan 2011
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    I’ve had a few chips on carbines and mid lengths and only found one lug cracked. A small chip doesn’t bother me but I keep an eye on it. Multiple chips and crack gets a replacement. They can fail at any round count but the few I have replaced saw about 10,000 rounds. There are too many factors to predict when it will fail.
    Remember, just because a lug shears doesn’t mean you are out of the fight. The gun can still work perfectly missing a lug. If I was in combat and one happened to shear, #1. I Probably wouldn’t know right then, #2. I Wouldn’t care even if I did know and keep shooting.
    Im not doubting Morpheus562 has seen a gun lock up due to the sheared lug... I’ve had some lock up due to hot ammo blowing a primer and it getting lodged in the FCG. It’s always a chance with anything happening with a machine and something can cause a jam.
    Always use your best judgment.
    Be aware I’m not advocating to keep using a rifle with a sheared lug, But lots of times one will break and the person doesn’t notice until they clean the rifle later on.
    Make inspecting the bolt part of your cleaning process and check headspace when you replace the bolt.
    Stay safe out there.
    -Ryan

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