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Thread: upper and lower fitting issues

  1. #1
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    upper and lower fitting issues

    Here's what I have:
    3 uppers, all the same model and from the same manufacturer
    3 lowers, all the same model and from the same manufacturer (different maker from the uppers)

    2 of the uppers fit properly with all 3 lowers.
    1 upper won't fit properly with any of the 3 lowers. I can slide the pivot pin in fine, but the takedown pin won't slide in all the way unless it is forced (hammered in) and I don't want to have to do that. If I reverse the process, I can slide the takedown pin in first without issues, but now the pivot pin won't slide in with finger pressure only. This happens with that particular upper and all 3 lowers.

    I sent the problematic upper back to the manufacturer with an RMA. Got an email back saying that they tried the upper with several other manufacturers lowers (except for a lower from the same company as the ones I have) and they all fit fine so they sent the upper back to me (awaiting delivery on my end).

    What least destructive means can I resort to in order to get this upper to fit with any of my lowers?

  2. #2
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    It does fit, it's just tight. Just tap the pin in! It will loosen up eventually. Most people would rather have an upper/lower fight that is extra tight vs extra loose.

    What's the manufacturer of the upper?
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  3. #3
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    Thank you. Mega lower with Vltor MUR-1A upper. You're right about better off starting tight and loose.

  4. #4
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    If you have to beat the takedown pin in place then something is out of spec. We just had an upper received in my San Diego class and it was out of spec at the rear where it meets with the lower at the top of the lower receiver extension. The company was contacted and it was replaced. In your case either the MUR is wrong or the lower is or you have a case of tolerance stacking.





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  5. #5
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    Re: upper and lower fitting issues

    Quote Originally Posted by grnamin View Post
    Thank you. Mega lower with Vltor MUR-1A upper. You're right about better off starting tight and loose.
    It will get easier as you shoot the gun and as the finish wears at the lugs. It will probably always be tight, but should get easier to break down. You could try to polish the inside of the lug with a fine abrasive like a scotch Brite pad or something similar if it's really driving you crazy.

  6. #6
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    Iraqgunz: Since the two other uppers fit all 3 lowers, I'm inclined to think that the non-fitting upper is a little out of spec, but not by much. Since Vltor won't repair or replace it, I'll go with the advice here and use it.

  7. #7
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    That's your choice. But, I will tell you that repeated beating of the rear pin in and out is going to cause wear inside the rear lug hole.

    I would try and fit it to the lower that has the least amount of issue.

    Quote Originally Posted by grnamin View Post
    Iraqgunz: Since the two other uppers fit all 3 lowers, I'm inclined to think that the non-fitting upper is a little out of spec, but not by much. Since Vltor won't repair or replace it, I'll go with the advice here and use it.





    "A firearm should be considered a fighting weapon first. Any other use should be considered a bonus." -Me

    Click here for Semper Paratus Arms AR15 armorer schedule/locations.

    M4C Misc. Training and Course Announcements- http://www.m4carbine.net/forumdisplay.php?f=141

    Multiple armorer certifications

    I am affiliated and work with SIONICS Weapon Systems in Tucson, AZ

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