Page 2 of 3 FirstFirst 123 LastLast
Results 11 to 20 of 23

Thread: upper and lower fitting issues

  1. #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?

  2. #12
    Join Date
    Jan 2008
    Location
    AZ-Waging jihad against crappy AR's.
    Posts
    21,051
    Feedback Score
    85 (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

  3. #13
    Join Date
    May 2012
    Location
    Plano, Texas
    Posts
    43
    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.

  4. #14
    Join Date
    Oct 2007
    Posts
    4,048
    Feedback Score
    4 (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.

  5. #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.

  6. #16
    Join Date
    May 2012
    Location
    Plano, Texas
    Posts
    43
    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.

  7. #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

  8. #18
    Join Date
    Aug 2009
    Location
    Kalifornia
    Posts
    126
    Feedback Score
    10 (100%)
    What is tolerence stacking?

    Thanks
    NRA Life Member Since 1993

  9. #19
    Join Date
    Dec 2012
    Location
    Southern WV
    Posts
    578
    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.

  10. #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 2 of 3 FirstFirst 123 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
  •