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Thread: Upper wear at cam pin pocket

  1. #11
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    once that area is black again, you've broken the rifle in.

  2. #12
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    Every upper I own has this type of wear. It is normal.

  3. #13
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    100% normal.
    Quote Originally Posted by scottryan View Post
    Anybody that owns or sells pistol versions of assault rifles is a bottom feeder, irregardless of the ban status of certain ammunition.

    They are illigetimate weapons that have no real purpose other than to attract retards to the gun community.

  4. #14
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    Thanks for all the replies. I had just not seen this level of wear so quickly in my other carbines/rifles, and just wanted to be sure that I was not missing something with my first SBR/can.

  5. #15
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    Jan 2012
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    I have just completed a MK18 build and while not worrying about the wear I do think that the removal of the anodizing occured faster than with my other 14.5" or 16" guns. FWIW I am using an H2 buffer and not shooting suppressed ... yet.

  6. #16
    Join Date
    Jun 2011
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    Totally normal about some "wear"...if it really bugs you..get a POF roll pin setup...but honestly...you wont need it

  7. #17
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    Quote Originally Posted by PD Sgt. View Post
    http://s783.beta.photobucket.com/use...tml?sort=3&o=0

    http://s783.beta.photobucket.com/use...tml?sort=3&o=1

    Here are links to the photos of the wear. I hope they work, not my strong point.

    I have no problem with wear, and I know it will occur on rails, etc., but this looks a little more like gouging (to the rear part of the pocket especially), and seemed outside the norm to me, though I could not get a good angle to show the extent of it in the pics. This is not the norm on my other carbines, but is present on one Colt. Again, if it is not a big deal, no worries, but I wanted to put it out there for a more experienced eye.

    Again, thanks for any help provided.
    You're fine. My 5.45 AR has more and it's rock solid.

  8. #18
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    I think you'll find that cam pin lash is the primary cause of the wear. If someone else can verify, I believe the TDP spec for the cam pin diameter and the hole in the bolt are nearly the same. To speed production and reduce returns, a manufacturer may make the hole to big or the pin to small.

    When the pin is too small or the hole to large, the unlocking force isn't lateral to rotation of the bolt and the pin rocks in the bolt hole. This leads to impact between surfaces (cam pin and upper receiver) and varying degrees of wear on the corners of the cam pin relief cut in the upper receiver.
    Last edited by MarkG; 03-20-13 at 10:57.

  9. #19
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    I agree this is a major contributor.

    An undersized diameter pin will also have more slop in the carrier cam track.

    The importance of cam pin tolerance seems to be lost on a lot of mfgs for this $5 part.



    Quote Originally Posted by MK18Pilot View Post
    I think you'll find that cam pin lash is the primary cause of the wear. If someone else can verify, I believe the TDP spec for the cam pin diameter and the hole in the bolt are nearly the same. To speed production and reduce returns, a manufacturer may make the hole to big or the pin to small.

    When the pin is too small or the hole to large, the unlocking force isn't lateral to rotation of the bolt and the pin rocks in the bolt hole. This leads to impact between surfaces (cam pin and upper receiver) and varying degrees of wear on the corners of the cam pin relief cut in the upper receiver.
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