Anyone Know The Profile Dimensions for the "Light" X39 Bbl?
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Thread: Anyone Know The Profile Dimensions for the "Light" X39 Bbl?

  1. #1
    XCR Guru Sean K.'s Avatar
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    Anyone Know The Profile Dimensions for the "Light" X39 Bbl?

    Looking at sending my 16" heavy bbl to ADCO to have it profiled to a light for $120.

    Problem is: ADCO does "medium" contour unless otherwise specified. Well, "medium" for an AR is .750" basically fore and aft of the gas block.

    Well, that's about the size of the heavy in the XCR.

    For comparison, a 5.56 "light" bbl in the XCR-L is ~.675" behind the gas block and ~.570" in front of it.

    Pretty sure I can't just tell ADCO to use those numbers since X39 is a .30 caliber round vs. .223.

    Not sure how much is safe to turn down so...does anyone have a "light" XCR-L X39 bbl they can mic for me?
    "Necessity is the plea for every infringement of human liberty. It is the argument of tyrants; the creed of slaves."-William Pitt the Younger

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    XCR Guru navalbeaver's Avatar
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    I've got one at the house. Without looking, I think it's tapered. I can get you some rough numbers in a few hours.

  3. #3
    XCR Guru navalbeaver's Avatar
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    There's a taper.

    Out of the barrel extension it's .975" for about a half inch or so then another half inch step down to .84", from there it's a constant taper for about 6.25" down to approx .72" before you get another step up for the gas block interface/journal. After the gas block it steps back down to .635" in front of the block down to approx .627" before it steps back up for the shoulder.

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  5. #4
    XCR Guru Sean K.'s Avatar
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    Quote Originally Posted by navalbeaver View Post
    I've got one at the house. Without looking, I think it's tapered. I can get you some rough numbers in a few hours.
    Much appreciated, Nate.
    "Necessity is the plea for every infringement of human liberty. It is the argument of tyrants; the creed of slaves."-William Pitt the Younger

  6. #5
    XCR Guru Sean K.'s Avatar
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    Quote Originally Posted by navalbeaver View Post
    There's a taper.

    Out of the barrel extension it's .975" for about a half inch or so then another half inch step down to .84", from there it's a constant taper for about 6.25" down to approx .72" before you get another step up for the gas block interface/journal. After the gas block it steps back down to .635" in front of the block down to approx .627" before it steps back up for the shoulder.
    Shoot...that sounds a lot more complicated than I'd hoped. I was hoping to just tell ADCO (for example, based on your numbers)...do a .72" after the gas block and .627" to the muzzle.

    I'm guessing RA has figured out there's a need for the taper on both sections.

    I guess I could just forward the info you gave and see if they can just follow something close to that approximation.

    I think bbls are $380-400 best price new anyway.....so buying a new one vs. getting this one contoured makes less sense.

    Hmmm....I'll have to think it over more.
    "Necessity is the plea for every infringement of human liberty. It is the argument of tyrants; the creed of slaves."-William Pitt the Younger

  7. #6
    XCR Guru mjorin's Avatar
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    I guess I didn't realize there was a light contour to the 7.62X39. I thought they were all heavy contour?
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  8. #7
    XCR Guru Sean K.'s Avatar
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    Quote Originally Posted by mjorin View Post
    I guess I didn't realize there was a light contour to the 7.62X39. I thought they were all heavy contour?
    It's a "newer" offering. Within the last couple of years IIRC. I'm basically just wanting to make the 16" as light as possible. If I do a 6.5G in this same rifle, I'll go light profile there as well. Trying to make something competitive in weight to my POF Revolution DI .308 since all my other .308s are freakin' pigs.
    "Necessity is the plea for every infringement of human liberty. It is the argument of tyrants; the creed of slaves."-William Pitt the Younger

  9. #8
    XCR Guru Sean K.'s Avatar
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    Nate, by chance do you have a weight on that light profile bbl? I'm assuming it has an A2 flash hider and Type 3 gas block, correct?

    Trying to figure out if it's even worth profiling the bbl over just leaving it as a heavy. I'll post up a weight on my bbl once I get home.
    "Necessity is the plea for every infringement of human liberty. It is the argument of tyrants; the creed of slaves."-William Pitt the Younger

  10. #9
    XCR Guru navalbeaver's Avatar
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    my scale says 2lb 1.5oz for the light profile. A2 and a type 1 gas block. For reference, a 5.56 light profile is 1lb 14.5oz. I didn't have a heavy profile readily accessible.
    Sean K. likes this.

  11. #10
    XCR Guru Sean K.'s Avatar
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    I sux. Didn't dig mine out of the safe last night since it's literally the last one in the back. I'll try and get a weight tonight...as well as the Type 3 vs. Type 1 block.

    Thanks very much for going to the trouble. If this place ever goes down, we're going to lose a lot of tech.
    Last edited by Sean K.; 01-08-2020 at 06:17 AM.
    "Necessity is the plea for every infringement of human liberty. It is the argument of tyrants; the creed of slaves."-William Pitt the Younger

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