Pennsylvania Firearm Owners Association
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  1. #1
    Join Date
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    Default AR bolt swapping

    I searched and didn't find anything on this so's...

    Recently I bought a backup AR bolt/carrier assy, and got to wondering:

    TM 9-1005-249-10 page 3-35, as well as every other FM I own, states:

    "WARNING DO NOT interchange bolt assemblies between rifles"

    No other supporting information is ever given.

    I'm pretty sure no armorer is going to scrap a perfectly serviceable bolt carrier because a bolt lug was cracked or a face pitted out of spec.

    What is the reasoning behind this oft repeated warning? Possible slide or cam binding? Legalities? I might well be missing something really simple, but it's escaping me.

    Thanks
    Last edited by SW357; February 5th, 2010 at 07:46 PM. Reason: cause I can't spele
    "In this world there's two kinds of people, my friend. Those with loaded guns, and those who dig.
    You dig." -Clint Eastwood

  2. #2
    Join Date
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    Folsom, Pennsylvania
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    Default Re: AR bolt swapping

    Head space is established by the bolt mating to the barrel extension. Both of those have tolerance. Mix and match parts and you can get a pairing that provides excess head space.

  3. #3
    Join Date
    Nov 2006
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    Default Re: AR bolt swapping

    Unless your bolt has 5000+ rounds through it I wouldnt be Really worried about it.


    BUT IF you are just go buy a set of Go/No-go gauges .

  4. #4
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    Default Re: AR bolt swapping

    It is just the Bolt, not the bolt carrier. The bolt by itself is an assembly (bolt, extractor, ejector, springs and retainers). You do not want to mix used bolts and barrels. A new bolt & a used barrel = GO, used bolt & new barrel = GO, used bolt & used barrel = NOGO. As the rifle is used the bolt lugs and receiver extension burnish each other as they wear into each other forming a uniform wear pattern between the two. A new bolt will wear into a used barrel and vice versa, but when they both have been used their wear patterns will not match and you greatly increase the potential for the wear to open up the headspace excessively. As long as at least one of the parts is new you should be fine, but it is still a good idea to check the headspace anyway.
    Last edited by Legion_Prime; February 5th, 2010 at 10:10 PM. Reason: Typo :D
    Warning: I may not read responses to OP before posting

  5. #5
    Join Date
    Dec 2008
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    Washington Crossing, Pennsylvania
    (Bucks County)
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    Default Re: AR bolt swapping

    Legion you make typo.


    .

  6. #6
    Join Date
    Nov 2008
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    Muhlenberg twp, Pennsylvania
    (Berks County)
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    Default Re: AR bolt swapping

    Quote Originally Posted by Legion_Prime View Post
    It is just the Bolt, not the bolt carrier. The bolt by itself is an assembly (bolt, extractor, ejector, springs and retainers). You do not want to mix used bolts and barrels. A new bolt & a used barrel = GO, used bolt & new barrel = GO, used bolt & used barrel = NOGO. As the rifle is used the bolt lugs and receiver extension burnish each other as they wear into each other forming a uniform wear pattern between the two. A new bolt will wear into a used barrel and vice versa, but when they both have been used their wear patterns will not match and you greatly increase the potential for the wear to open up the headspace excessively. As long as at least one of the parts is new you should be fine, but it is still a good idea to check the headspace anyway.
    fixed and +1

  7. #7
    Join Date
    May 2008
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    Good ol' Fredericksburg, Pennsylvania
    (Lebanon County)
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    Default Re: AR bolt swapping

    Much appreciated.

    And that trips my limit-of-1-per-year breach of the "three most difficult words" rule.
    "In this world there's two kinds of people, my friend. Those with loaded guns, and those who dig.
    You dig." -Clint Eastwood

  8. #8
    Join Date
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    Default Re: AR bolt swapping

    Quote Originally Posted by RaisedByWolves View Post
    Legion you make typo.


    .
    Hahahaha I did!

    Quote Originally Posted by busa dave View Post
    fixed and +1
    Whoops! Thanks for catching that guys, I'll go correct that right now.
    Warning: I may not read responses to OP before posting

  9. #9
    Join Date
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    Northampton County, Pennsylvania
    (Northampton County)
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    Default Re: AR bolt swapping

    So a new bolt is good in any AR barrel? Even with 20K down the tube? I did not know that. Please confirm. That's very helpful if true.

  10. #10
    Join Date
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    Default Re: AR bolt swapping

    Quote Originally Posted by ungawa View Post
    So a new bolt is good in any AR barrel? Even with 20K down the tube? I did not know that. Please confirm. That's very helpful if true.
    Well considering 20K would be nearing the end of the barrels service life I'd replace them both. So after 4 bolts, get a new barrel to go with the fifth. That's just approximate by barrel length for a 16" carbine, adjust approximate service life in proportion with the barrel and gas system length (eg longer barrel/gas system = longer service life.)
    Warning: I may not read responses to OP before posting

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