Replacing 39(A,M,D) Barrel and indexing
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Thread: Replacing 39(A,M,D) Barrel and indexing



  1. #1
    Tenderfoot
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    Replacing 39(A,M,D) Barrel and indexing

    As much as I have searched, I can not find any info on the proper Installation of a new(different) barrel on a 39 action.
    I want to install my oct shorty barrel on my 39A action, then top it off with Boyds "pepper" laminate stock.

    I have a large vise and wood barrel blocks, Fabbing up a action wrench, so removing the old barrel will not be a problem.

    Question is, how do you "index" the new barrel to the action?? (make sure the sites are straight up when the barrel threads tighten.
    then how do you set the head space once the barrel is installed?

    Thanks,
    Slack
    GITU1 likes this.

  2. #2
    Gunfighter
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    I am assuming (could be my mistake) that the barrel is already chambered. If so the headspace should be off of the 22 rim and already set. One way that I have indexed barrels is to use 2 ea. 3 ft. long pieces of 1/4 inch square stock (from lowes or home depot). Clamp the receiver/barrel in a vise. I tap the front sight out of the barrel and balance one at the midpoint of the square stock in the dove tail and balance the midpoint of the other on top of the back of the receiver. Step back a few feet and look down the barrel from the bore end. When it is indexed properly, you will only see one piece of square stock.
    turbobug likes this.
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  3. #3
    Gun Wizard
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    Quote Originally Posted by Slackdaddy View Post

    Question is, how do you "index" the new barrel to the action??
    Not even Remington knows how to do that consistently.

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  5. #4
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    These are threaded into the action. Typically - a "new" barrel would be fitted onto the receiver and torqued down. Mark the top and bottom. Then you would match mark the barrel to the receiver. Unscrew it, cut all your chamber extractor and ejector slots, dovetails and slots for the sights, tube, barrel bands, and wood mounting. Then finish up the finish and screw it back on. Viola!

    This is probably the sort of thing you would leave for a pro gunsmith who deals with these sort of things regularly - because you can twist your receiver or really mess up things if you don't have the right tools.

  6. #5
    Tenderfoot
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    This is a "New" to this receiver barrel.
    Not a new barrel blank.
    What I was wondering is,, is the marlin receivers and barrels machine to such exacting tolerances, that when you screw the "new to me" barrel into the receiver and tighten it up, the barrel will end up correctly indexed, with all the sight and ejector groves in the correct relation to the receiver??
    If not,, how is the replacement barrel "indexed"??

  7. #6
    Gun Wizard
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    only way to tell is to screw it in and see where the dovetails/sights are when tight. I've watched an expert do barrel change but never done it

  8. #7
    Tenderfoot
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    So you have seen them do it??
    When it does not exactly line up after tightening,, how is it adjusted? are there shim stock washers to get it to move clockwise? how about getting it to move the other way, THAT is my question.
    I have scoured the internet for days, yet this appears to be a deep, dark, lost secret??

    Quote Originally Posted by Goldtrigger View Post
    only way to tell is to screw it in and see where the dovetails/sights are when tight. I've watched an expert do barrel change but never done it
    turbobug likes this.

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    Quote Originally Posted by Slackdaddy View Post
    This is a "New" to this receiver barrel.
    Not a new barrel blank.
    What I was wondering is,, is the marlin receivers and barrels machine to such exacting tolerances, that when you screw the "new to me" barrel into the receiver and tighten it up, the barrel will end up correctly indexed, with all the sight and ejector groves in the correct relation to the receiver??
    If not,, how is the replacement barrel "indexed"??
    Hope for the best but plan for the worst. It may be fine, it may not. The only way to know is to torque the barrel on and see.

    This is where you would like a gunsmith with some experience with this sort of thing.

  10. #9
    Tenderfoot
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    I am hoping once torqued down it will be "Indexed"
    BUT, I am planning for the worse.
    I am capable, I have the tools/shop to perform most any work, BUT I need to know the method or procedure to adjust the indexing.


    Quote Originally Posted by truckjohn View Post
    Hope for the best but plan for the worst. It may be fine, it may not. The only way to know is to torque the barrel on and see.

    This is where you would like a gunsmith with some experience with this sort of thing.

  11. #10
    Esteemed Sharpshooter
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    I would use smooth round barrel & put a scope on it then no worries over index.
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