Page 1 of 2 12 LastLast
Results 1 to 20 of 23

Thread: upper and lower fitting issues

  1. #1
    Join Date
    May 2012
    Location
    Plano, Texas
    Posts
    40
    Feedback Score
    0

    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
    Join Date
    Sep 2010
    Posts
    755
    Feedback Score
    0
    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?
    Quote Originally Posted by skd_tactical View Post
    It's a shot in the dark ... I have a better chance of guessing when my wife will be mad for no reason.
    "If your not using an aimpoint, you need to take a ****ing piss test." -LAV

  3. #3
    Join Date
    May 2012
    Location
    Plano, Texas
    Posts
    40
    Feedback Score
    0
    Thank you. Mega lower with Vltor MUR-1A upper. You're right about better off starting tight and loose.

  4. #4
    Join Date
    Jan 2008
    Location
    AZ-Waging jihad against crappy AR's.
    Posts
    20,009
    Feedback Score
    80 (100%)
    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.





    "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

  5. #5
    Join Date
    Jun 2006
    Location
    GA
    Posts
    2,875
    Feedback Score
    35 (100%)

    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
    Join Date
    May 2012
    Location
    Plano, Texas
    Posts
    40
    Feedback Score
    0
    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
    Join Date
    Jan 2008
    Location
    AZ-Waging jihad against crappy AR's.
    Posts
    20,009
    Feedback Score
    80 (100%)
    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

  8. #8
    Join Date
    May 2012
    Location
    Plano, Texas
    Posts
    40
    Feedback Score
    0
    Quote Originally Posted by Iraqgunz View Post
    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.
    Good call. I will try that first.

  9. #9
    Join Date
    Feb 2013
    Location
    U.S.
    Posts
    2,304
    Feedback Score
    1 (100%)
    If I have a new carbine with tight upper to lower fit, I place the bottom of the pistol grip on my workbench and press down on top of the rear of the carry handle to get the rear take down pin to go in. A little dab of lightweight grease on the rear take down pin helps. I push down on top of the carry handle and use a delrin pin to push out the take down pin for disassembly.

    I would never pound on anything with a hammer to get the rear take down pin to go in.
    Last edited by T2C; 08-06-13 at 15:37.
    Every man needs a M1 Garand and 1903 Springfield rifle. Recoil is a good thing.

  10. #10
    Join Date
    Oct 2007
    Posts
    3,739
    Feedback Score
    2 (100%)
    My advise is sell the offending part and don't buy from that company anymore. Been there, done that. It's what it finally took to get me to stop drinking Noveske Kool-Aid.

  11. #11
    Join Date
    Feb 2012
    Posts
    102
    Feedback Score
    0
    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.
    Why wont Vltor fix the issue?

  12. #12
    Join Date
    Jan 2008
    Location
    AZ-Waging jihad against crappy AR's.
    Posts
    20,009
    Feedback Score
    80 (100%)
    Possibly because it is within THEIR specs. They have no control over the lowers or the possibility of tolerance stacking.

    I agree that I would contact them again and CLEARLY explain the issue.

    Quote Originally Posted by STONE-YARDER View Post
    Why wont Vltor fix the issue?





    "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

  13. #13
    Join Date
    May 2012
    Location
    Plano, Texas
    Posts
    40
    Feedback Score
    0
    Quote Originally Posted by STONE-YARDER View Post
    Why wont Vltor fix the issue?
    They tested the upper with several other manufacturer's lowers (but not Mega) and the upper fit fine. The upper was sent back to me (waiting for it to arrive) before I could respond to their email reply regarding the tests.

    I would stress again that I have 2 other MUR-1A's that fit all 3 Mega lowers properly. Maybe I should have sent the Mega lower as well so that they could see the issue firsthand, but I didn't know if the lower would require FFL transfers.

  14. #14
    Join Date
    Oct 2007
    Posts
    3,739
    Feedback Score
    2 (100%)
    Quote Originally Posted by grnamin View Post
    They tested the upper with several other manufacturer's lowers (but not Mega) and the upper fit fine. The upper was sent back to me (waiting for it to arrive) before I could respond to their email reply regarding the tests.

    I would stress again that I have 2 other MUR-1A's that fit all 3 Mega lowers properly. Maybe I should have sent the Mega lower as well so that they could see the issue firsthand, but I didn't know if the lower would require FFL transfers.
    Who cares what it fits? You mic the lugs and if it's within mil-spec, it's you're problem. If it's not, it's a manufacturing defect.

  15. #15
    Join Date
    Dec 2010
    Location
    Chicago, IL
    Posts
    197
    Feedback Score
    0
    Just to state the obvious... You don't have one of those little red wedges do you?
    NRA Life Member, ISRA Member, American GunSmith Institute Certified GunSmith, State of IL Certified Carry Concealed Instructor, NRA Instructor, NRA RSO.

    I do not suffer from TTD, Top Tier Disease.

  16. #16
    Join Date
    May 2012
    Location
    Plano, Texas
    Posts
    40
    Feedback Score
    0
    Quote Originally Posted by CGS View Post
    Just to state the obvious... You don't have one of those little red wedges do you?
    No red wedges.

  17. #17
    Join Date
    Jul 2011
    Posts
    31
    Feedback Score
    0
    The only way to 100% avoid tolerance stacking issue is to buy a fitted upper and lower from the same factory. It would usually be advertised as fitted.

    If it fits, even if it requires some force, but you can take the rear pin in and out at the field, I wouldn't worry about it.
    Precision Delivery Systems (www.pdsrifles.com) Like us on Facebook
    Multi-Coastal Enterprises, LLC

  18. #18
    Join Date
    Aug 2009
    Location
    Kalifornia
    Posts
    119
    Feedback Score
    10 (100%)
    What is tolerence stacking?

    Thanks
    NRA Life Member Since 1993

  19. #19
    Join Date
    Dec 2012
    Location
    Southern WV
    Posts
    564
    Feedback Score
    0
    Quote Originally Posted by uniform64 View Post
    What is tolerence stacking?

    Thanks
    Tolerance stacking is a characteristic of mass production. If the pivot/takedown hole distance in the upper is at the far end of the tolerance and the holes in the lower are at the near end, along with all 4 bores being at their maximum material condition(MMC, small), then it may be that the pins will not slide into place(slip fit). Pounding the pins into place indicates an interference fit, an undesirable condition.

  20. #20
    Join Date
    Jul 2011
    Posts
    31
    Feedback Score
    0
    Here is an example. S I want to machine my own AR-15 hammer, but I don't want to use a blueprint. So I ask a friend to mold his hammer part and send it to me. Then I take a pair of calipers and take the measurements, and do my own drawing. Then I get on a CNC machine and make the part.

    Say the mold was only accurate to +-0.02" (Just example numbers here)
    The calipers were calibrated and rated to be accurate to +- 0.01"
    Then say my CNC machine will machine parts to 0.02" accuracy.
    Then the dimensions of my finished part may be up to 0.05" off. Because the tolerances were stacked.

    Theoretically that doesn't mean the part will be off by whatever the total sum comes out to be (in this case, 0.05), but it can be that much off.

    I don't really know what the industry does to manufacture these receivers, but potentially something like this can happen:
    Brand A and B are AR-15 receiver manufacturers. They each use a different point in the part to measure the dimensions. So Brand A has holes that tend to be off towards the forward part of the rifle, but brand B tends to go other way. Even though both manufacturers made both parts within milspec tolerances, the upper may be out of spec with the lower.

    In reality I think most manufacturers generally machine things the same way; there may be differences in material, overall tolerances, quality control, etc. But an example like above where tolerances can stack isn't going to happen between most manufacturers.

    My personal experience is the same. I've also not had many customers complaining about parts not fitting between different manufacturers. But I still may be wrong, so please take this bit with a grain of salt.
    Precision Delivery Systems (www.pdsrifles.com) Like us on Facebook
    Multi-Coastal Enterprises, LLC

Page 1 of 2 12 LastLast

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •