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Thread: Current BCM Upper Barrel Fit

  1. #1
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    Current BCM Upper Barrel Fit

    I’m drawing up a precision DMR type build on paper And doing my research before I start buying. Been reading up on barrel fit and bedding. Looking up BCM receivers and they have this in their description:

    Built to the correct Mil-Specs
    (Inside Diameter for barrel extension slightly undersized for a tighter fit to the barrel and a more accurate rifle. Please use a heat gun or hair dryer to warm up threaded bore of receiver if barrel extension is too tight.)


    Has anyone had experience with this? Does this negate the need for bedding? Thanks
    Last edited by OldState; 12-08-19 at 13:24.
    "A flute without holes, is not a flute. A donut without a hole, is a Danish." - Ty Webb

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    I don't know if bedding would still be beneficial but I can confirm the 3 I have used soon had a very tight fit and needed heat to get the barrel in. I put the barrel in my freezer for one if them that was a little tighter than the others

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    3 for 3 on requiring heating also.

    Just became aware this week White Oak claims to oversize their barrel extensions 0.001" versus others which has me curious how a BCM would interact with such an extension.

  4. #4
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    Yes, undersized bores or oversized extensions will generally require heat to to assemble.

    This tight shrink fit is generally good from an accuracy standpoint and should eliminate the need for any bedding.
    Black River Tactical
    BRT OPTIMUM Barrels - 16" MPR, 14.5" MPC, 11.5" CQB, 9" PDW
    BRT OPTIMUM-S Barrel - 11.5" CQB Suppressor Gas Drive
    BRT OPTIMUM-S Barrel - 11.5" SB Suppressor, 11.5" SBT 25 Deg Tapered Shoulder Suppressor
    BRT Covert Comps 7.62, 5.56, 6X, 9mm
    BRT MarkBlue Gas Tubes - BRT EXT, EXC and PDW Lengths
    BRT EZTUNE Gas Tubes - CAR and MID
    BRT MicroPin Gas Blocks - .750" & .625"
    BRT MicroTUNE Adjustable Gas Blocks
    BRT CustomTUNE Gas Ports

  5. #5
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    Quote Originally Posted by Clint View Post
    Yes, undersized bores or oversized extensions will generally require heat to to assemble.

    This tight shrink fit is generally good from an accuracy standpoint and should eliminate the need for any bedding.
    Clint, You seem to be well respected here.. What does one really gain by bedding the extension? Real world benefits for the guy shooting quality factory ammunition with a trigger safe enough for real world use. I understand it may be a psychological advantage if your that kind of guy. I know I wouldn't benefit from doing it but I am the guy happy to shoot 6 inch groups with green tips off of an improvised rest with a six pound rifle!!

  6. #6
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    Quote Originally Posted by jsbhike View Post
    3 for 3 on requiring heating also.

    Just became aware this week White Oak claims to oversize their barrel extensions 0.001" versus others which has me curious how a BCM would interact with such an extension.
    Good to know. White Oak was a barrel I was considering.

    If the BCM receivers are as tight as described I guess bedding or shimming would be pointless.
    "A flute without holes, is not a flute. A donut without a hole, is a Danish." - Ty Webb

  7. #7
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    I have used a heat gun and fitted two of them with no issues. That is only a sample size of two, for what that is worth.

  8. #8
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    It's hard to directly establish the gains from a good fit, but eliminating variables is always good for consistency.

    Some sources claim 1/3 reduction in group size.

    Dirt shooters won't appreciate the effort required to achieve a good fit.

    Here is a great discussion on techniques for accurizing ARs.

    https://www.m4carbine.net/showthread...-Accurizing-AR



    Quote Originally Posted by GH41 View Post
    Clint, You seem to be well respected here.. What does one really gain by bedding the extension? Real world benefits for the guy shooting quality factory ammunition with a trigger safe enough for real world use. I understand it may be a psychological advantage if your that kind of guy. I know I wouldn't benefit from doing it but I am the guy happy to shoot 6 inch groups with green tips off of an improvised rest with a six pound rifle!!
    Black River Tactical
    BRT OPTIMUM Barrels - 16" MPR, 14.5" MPC, 11.5" CQB, 9" PDW
    BRT OPTIMUM-S Barrel - 11.5" CQB Suppressor Gas Drive
    BRT OPTIMUM-S Barrel - 11.5" SB Suppressor, 11.5" SBT 25 Deg Tapered Shoulder Suppressor
    BRT Covert Comps 7.62, 5.56, 6X, 9mm
    BRT MarkBlue Gas Tubes - BRT EXT, EXC and PDW Lengths
    BRT EZTUNE Gas Tubes - CAR and MID
    BRT MicroPin Gas Blocks - .750" & .625"
    BRT MicroTUNE Adjustable Gas Blocks
    BRT CustomTUNE Gas Ports

  9. #9
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    Quote Originally Posted by Clint View Post
    It's hard to directly establish the gains from a good fit, but eliminating variables is always good for consistency.

    Some sources claim 1/3 reduction in group size.

    Dirt shooters won't appreciate the effort required to achieve a good fit.

    Here is a great discussion on techniques for accurizing ARs.

    https://www.m4carbine.net/showthread...-Accurizing-AR

    Thanks for that video! The other vids they have on their channel are interesting as well. 2 1980's matches they had featured reholstering and obstacle negotiation which were interesting.

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    Quote Originally Posted by jsbhike View Post
    Thanks for that video! The other vids they have on their channel are interesting as well. 2 1980's matches they had featured reholstering and obstacle negotiation which were interesting.
    Looks like the bedding isnt necessary.

    @Clint

    What are your thoughts on lapping the receiver face? I have seen a few examples of where users have said this is beneficial, but have personally never done this

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