Shimming AR Barrel Extension

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  • bstewrat3

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    Apr 26, 2009
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    Beech Grove
    I am in the process of assembling a 6.5 Grendel AR and have been taking a more in depth look at getting as much accuracy as possible out of it. While looking at ways of tightening up the fit of the barrel extension into the upper receiver, I came across the use of stainless steel shim stock. Has anyone used this method? I originally considered using the locktite method, but would much prefer to try the shims. If anyone knows of a local source for smaller amounts of .001-.005 I would be interested in that as well.
     

    NyleRN

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    Dec 14, 2013
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    Scottsburg
    I've read about folks doing it for the purposes of accuracy but I think in order to get the full benefit you need to lap/square off the face of the front upper receiver
     

    bstewrat3

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    I've read about folks doing it for the purposes of accuracy but I think in order to get the full benefit you need to lap/square off the face of the front upper receiver

    I will be lapping the face of the receiver. I am wanting to bring the diameter of the barrel extension up to the point where it will not slip fit into the receiver without heating the receiver first.
     

    natdscott

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    Jul 20, 2015
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    .
    You don't need metal shims.

    Two options:

    1) Get a BCM upper with smaller ID, or a WOA or BAT extension with a larger OD. (NOT both).

    2) Glue it with Red loctite. Cure vertically.


    There sure are a bunch of us with 1/2 Minute guns that were glued into just reg'lar uppers with reg'lar extensions....


    -Nate
     

    BiscuitsandGravy

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    At the Ranch.
    You don't need metal shims.

    Two options:

    1) Get a BCM upper with smaller ID, or a WOA or BAT extension with a larger OD. (NOT both).

    2) Glue it with Red loctite. Cure vertically.


    There sure are a bunch of us with 1/2 Minute guns that were glued into just reg'lar uppers with reg'lar extensions....


    -Nate

    2nd that. The only time I've used shims is to fix the timing of a stubborn bbl nut. YMMV.
     

    INhondo

    Plinker
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    Mar 5, 2012
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    Greenwood
    I've glued one build (.22 Rimfire conversion) with high temperature Loctite and shimmed another (DPMS .308) with 0.001" S/S shim material. It didn't take much time for either process and I can see no drawbacks to doing either one. I also don't see any problem if someone doesn't want to do either process. I have a factory built Bushmaster 5.56 with neither process done and it shoots better than I'm capable of utilizing.
     

    rob63

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    May 9, 2013
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    I shimmed mine. It was part of the initial build, so no before photos, but I am very happy with the results.

    Grainger Industrial Supply is where I found the correct thickness of metal.
     

    bstewrat3

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    Apr 26, 2009
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    Beech Grove
    Just a follow up. I shimmed mine with .001 stainless feeler gauge which would not allow the barrel to slide into the upper receiver. I cooled the barrel and feeler gauge, and heated the upper just around the thread area to cause it to expand just enough to slide the barrel and feeler gauge in. They bonded almost immediately and cannot be separated by hand. I am currently in the shoot one and clean phase of my barrel brake in so no groups yet.
     
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