Mental Masturbation: XCR-M in something other than .308
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Thread: Mental Masturbation: XCR-M in something other than .308

  1. #1
    XCR Guru Sean K.'s Avatar
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    Mental Masturbation: XCR-M in something other than .308

    So the options are .243 Win, .260 Rem or 6.5 CM.

    The 6.5CM seems to be the latest/greatest....but I've read/heard they burn up bbls in a few thousand rounds. What I don't understand is why....

    Max SAAMI chamber pressures are 60K, 60K, and 62K respectively....with .308 having a 62K max as well. All of them run 1/8 twist bbls from RA....(except .308 which is a 1/10)....assuming the website builder is correct.

    You get decent bbl service life out of .308....and it has similar pressure and more twist, which should make it worse. Are the .243 and .260 also subject to wearing out bbls faster than .308 or is this more a 6.5CM issue?...and does anyone know why? Is the bbl wear throat erosion maybe?

    Do all of them feed from a standard .308 Pmag without issue (I'm assuming you might have to get the M118 LR models for the extra length of the 6.5CM cartridge)?

    Are these conversions/uppers even available? I know 6.5CM exists....not sure about the other two, so this may be just theoretical discussion anyway.

    As the title suggests, I'm really just kind of thinking about it. I'd probably be forced to get into reloading to get any of the above calibers and from what I read of XCR-M accuracy for most folks....I'm not sure it's a good platform for 8-1K yard precision shooting anyway, but I do love the platform and all this talk of better ballistics from 6mm ARC in L sized and AR15 platforms makes me wonder about sizing up to the -M or AR10 in one of these calibers.

    Any input appreciated.
    "Necessity is the plea for every infringement of human liberty. It is the argument of tyrants; the creed of slaves."-William Pitt the Younger

  2. #2
    XCR Guru TexasChris's Avatar
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    I'm pulling this from a long way back, iirc, the 6.5 throat erosion is caused by shoulder angle. My 6.5 does feed from standard 30 cal pmags.

    As much as I like the platform, a 2 MOA or worse rifle would likely get very, very frustrating around 600 yards......and with so many good AR's in 6.5, 6, 260, Valkyrie, and now the arc.......sproing.
    Sean K. and fmunk like this.
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    XCR Guru fmunk's Avatar
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    Because of the title I thought I was going to see some eye candy... kinda disappointed.
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  5. #4
    XCR Guru Sean K.'s Avatar
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    Quote Originally Posted by fmunk View Post
    Because of the title I thought I was going to see some eye candy... kinda disappointed.
    Sorry to disappoint.
    "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 TomAiello's Avatar
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    Sean, what do you see 6.5 CM giving you that 6.5 G doesn't? A little more range and energy at that range? With the XCR triggers and barrels, will the extra range be useable?
    - Tom Aiello
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    XCR Guru Sean K.'s Avatar
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    Quote Originally Posted by TomAiello View Post
    Sean, what do you see 6.5 CM giving you that 6.5 G doesn't? A little more range and energy at that range? With the XCR triggers and barrels, will the extra range be useable?

    That's it. More range and energy.

    I bought 2 L and 1 M bbl extensions....so a custom bbl isn't out of the question; not that I think that will significantly improve the accuracy.

    I'm not even sure I'll go through with this. The 6mm ARC and some recommendations about .243 Winchester had me just mulling over the -M chassis and things that are available for it.
    "Necessity is the plea for every infringement of human liberty. It is the argument of tyrants; the creed of slaves."-William Pitt the Younger

  8. #7
    XCR Guru TexasChris's Avatar
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    Quote Originally Posted by Sean K. View Post
    That's it. More range and energy.

    I bought 2 L and 1 M bbl extensions....so a custom bbl isn't out of the question; not that I think that will significantly improve the accuracy.

    I'm not even sure I'll go through with this. The 6mm ARC and some recommendations about .243 Winchester had me just mulling over the -M chassis and things that are available for it.
    Bro, I'm right there with you. If Alex could deliver on the accuracy, it would be awesome. So much potential in the package.......

    Get that owtlaw guy who always pops up on accuracy threads with his custom shop, hand rolled, sub moa, BFF BS to order one for you.

    Shoot, get him to order you 2.
    Sean K. likes this.
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  9. #8
    XCR Guru Sean K.'s Avatar
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    Quote Originally Posted by TexasChris View Post
    Bro, I'm right there with you. If Alex could deliver on the accuracy, it would be awesome. So much potential in the package.......

    Get that owtlaw guy who always pops up on accuracy threads with his custom shop, hand rolled, sub moa, BFF BS to order one for you.

    Shoot, get him to order you 2.
    And I wonder how much of the seeming accuracy issue is attributable to the bbl attachment set up. Also wonder if additional points of contact would help....like recessed allens on the left/right side of the receiver into the extension.

    Guys re-bed their ARs to improve accuracy...I wonder if the old "shim" wrap the bbl extension to get it to be a super tight fit would work in this case as well...though the bbl screw would have to be accounted for in the shim.

    I know RA has made that fit up A LOT tighter than it used to be...my 6.5G is so tight you can't pull the bbl without using the charging handle and bcg (minus the bolt) to drive the bbl out of the gun when you want to pull it. I haven't tested that one for accuracy yet as I'm still trying to figure out the feeding issue. Just bought a bunch of Elanders to see if it's all mag related and I finally got my warrantied 6.5G mags back from ASC. Want to get out and shoot it, but it's damn hot right now and I need to make a bunch of new target stands that I've been putting off.
    "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 TomAiello's Avatar
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    Let us know how the E-Landers work for you. I've been out the last two days trying to work through magazine/ammo/suppressor/malfunction combinations (on an AR-9 that takes Glock magazines), and I know how frustrating that is.
    - Tom Aiello
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    ...I don't care, I'm still free, you can't take the sky from me...

  11. #10
    XCR Guru TexasChris's Avatar
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    Quote Originally Posted by Sean K. View Post
    I know RA has made that fit up A LOT tighter than it used to be....
    Has to be one of the critical elements.
    Do what you've always done, get what you've always got. ----- Have gun. Will travel.

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