View Poll Results: Round count and bolt failures with mid-length gas systems.

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  • Bolt failed under 2,500 rounds

    4 4.26%
  • Bolt failed under 5,000 rounds

    2 2.13%
  • Over 5,000 rounds with no bolt failure

    56 59.57%
  • Bolt failed under 10,000 rounds

    3 3.19%
  • Over 10,000 rounds with no bolt failure

    17 18.09%
  • Bolt failed under 15,000 rounds

    0 0%
  • Over 15,000 rounds with no bolt failure

    2 2.13%
  • Bolt failed under 20,000 rounds

    0 0%
  • Over 20,000 rounds with no bolt failure

    6 6.38%
  • Bolt failed: unknown number of rounds

    4 4.26%
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Thread: Who has broken a bolt with a mid-length gas system?

  1. #51
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    Not a midlength, but someone mentioned Colt. I broke a Colt bolt at the cam pin hole on my 1st 6933 I believe somewhere between 4-5k. Nearly half of that suppressed.

  2. #52
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    I am bumping this to see if anyone has new data to add to the poll.

  3. #53
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    I haven’t owned a mid-length in a few years but I have a few Colt 6920 bolts go over 15K, until the barrel was replaced, without issue.

  4. #54
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    BCM midlength, 16-inch, Aero Precision bolt. Around 6,000 rounds, much of it fired in rapid semi-auto or at the cyclic rate (binary trigger). Firing schedule is in clusters as I don't always have the time to get out and train. Firing schedule has been conducted in all manner of conditions (100+ degree summers, in rain, and subzero temps in the winter, with snow). Upper is about two years old. No sign of failure, no malfunctions thus far.

  5. #55
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    I am going to go out on a limb here and state that the M16/AR bolt is not as fragile as many people seem to think it is.

    10,000 to 12,000 should be around the average life. And yes, since that is an average, there will be some that fail early, but they will be balanced out by some that last longer.

    Replacing your bolts at 5,000 rounds is silly.

  6. #56
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    So, assuming a ~25k round barrel life for a quality chrome barrel, a more reasonable service schedule might be to replace the bolt once around the 10k mark and then retire the second bolt and barrel together.

    Sound about right?

    Quote Originally Posted by lysander View Post
    I am going to go out on a limb here and state that the M16/AR bolt is not as fragile as many people seem to think it is.

    10,000 to 12,000 should be around the average life. And yes, since that is an average, there will be some that fail early, but they will be balanced out by some that last longer.

    Replacing your bolts at 5,000 rounds is silly.
    Black River Tactical
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  7. #57
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    Quote Originally Posted by Clint View Post
    So, assuming a ~25k round barrel life for a quality chrome barrel, a more reasonable service schedule might be to replace the bolt once around the 10k mark and then retire the second bolt and barrel together.

    Sound about right?
    I advocate replace on inspection failure. Every range outing, clean the bolt head and look at it. Cracks will be visible to the naked eye at least 500 to 1000 rounds before actual failure (if you use a 10X magnifier, you will get a little more warning). You don't have to inspect all of the lugs, the two flanking the extractor are the highest stressed and will fail first, and the thin sections around the cam pin hole.

    Since that 10 to 12 K is an average, some might show cracking as early as 6 or 8 thousand, depending on ammunition, gas system and firing schedule. If you replace a barrel at anything over 15 K and the bolt is original to that barrel, it would not be too a dumb idea to retire the bolt with the barrel.

    This is a magnetic particle, but the indicated cracks are visible to the naked eye. This particular bolt, with three cracks you can see shot another 4,000 rounds before actually shedding one of the cracked lugs.

    Attachment 66979

    You have plenty of time to inspect and replace bolt before they break on you.
    Last edited by lysander; 12-15-21 at 09:59.

  8. #58
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    Quote Originally Posted by lysander View Post
    Since that 10 to 12 K is an average, some might show cracking as early as 6 or 8 thousand, depending on ammunition, gas system and firing schedule.
    I'm curious, what ammunition, gas systems, and firing schedules do *you* think are harder on a bolt?

    Joe Mamma
    "Reliability above all else"
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  9. #59
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    Quote Originally Posted by Joe Mamma View Post
    I'm curious, what ammunition, gas systems, and firing schedules do *you* think are harder on a bolt?

    Joe Mamma
    Not Lysander, but I would think m855a1, carbine gas, and lots of full auto.
    “You have made us for yourself, O Lord, and our heart is restless until it rests in you.” -Augustine

  10. #60
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    Quote Originally Posted by Joe Mamma View Post
    I'm curious, what ammunition, gas systems, and firing schedules do *you* think are harder on a bolt?

    Joe Mamma
    The shortest gas system, the hottest ammunition out there, and the fastest shooting possible.

    Quote Originally Posted by georgeib View Post
    Not Lysander, but I would think m855a1, carbine gas, and lots of full auto.
    Yup, this is probably the hottest stuff available, and that would be the fastest.

    Although, a pistol length system would probably be rougher than a carbine system.
    Last edited by lysander; 12-16-21 at 07:02.

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