AR15 upper is too big to fit into lower

Discussion in 'GSSF' started by emt1581, Mar 5, 2010.

  1. emt1581

    emt1581 Curious Member

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    I'm not sure how to fix the issue. I mean would a Dremmel fix this problem?

    Anyways, I tried putting my YHM upper into a ShARps lower. It didn't fit. I figured "Great, I bought a bunch of these and they are all POS!" But then I tried the upper in my SA and Stag lowers...didn't fit.

    Now the upper does fit snugly in one or two of my other lowers, but I'd like it to fit as it should in ALL my lowers. Is this a problem that can be (easily) fixed? Should I just put it in whichever lower it fits in?

    EDIT: I forgot to explain WHERE it doesn't fit. It's the rear point (not sure of the correct name) where the rear pin locks the upper to the lower.

    Thanks!

    -Emt1581
     
    Last edited: Mar 5, 2010
  2. mad.gunsmith

    mad.gunsmith NRA and GSSF Life Member

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  3. Blitzer

    Blitzer Cool Cat

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    Find technical drawings for the upper and lower and modify the upper to be within specifications. Or contact the uppers manufacturer and exchange them?:dunno::whistling:
     
  4. emt1581

    emt1581 Curious Member

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    Well I do have a set of calipers I use for reloading. If there is a standard measurement this part should be I can see how far off this thing it.

    But is there any danger or problem with using an oversized part like that in a lower that will tolerate it?

    Thanks!

    -Emt1581
     
  5. faawrenchbndr

    faawrenchbndr CLM

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    The problem is this,.....once you start grinding on a lower or an upper, the hard annodizing is removed.
    This effectively destroys the hard outter coating, think of it as removing the heat treating of steel.
     
  6. faawrenchbndr

    faawrenchbndr CLM

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    Pm me your e-mail address, I can send you a print.
     
  7. harleyfx69

    harleyfx69

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    usually before you get a chance to shoot the combo, or just take it down a few times they are a bit tight,

    but they should go in,

    if its a yankee hill machine upper, i would say that is almost guaranteed to be in spec, but your unknown lowers, would be in question,

    might see if the finish is a bit thick down there,

    but other than that use sand paper really lightly,

    or consider sending it back to the factory
     
  8. emt1581

    emt1581 Curious Member

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    But is there anything potentially dangerous about an upper that is minimally larger than spec?

    Thanks!

    -Emt1581
     
  9. harleyfx69

    harleyfx69

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    i just looked at one of my uppers,

    and there is rub / wear on that point on the upper,

    you might just try oiling it a bit and working it into the lower
     
  10. emt1581

    emt1581 Curious Member

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    I could be missing it but on the print at G.5/8.5 where the space is, there is no measurement for it. :dunno:

    Do you know the rear part I mean, where the upper locks into the lower?

    Thanks!

    -Emt1581
     
  11. faawrenchbndr

    faawrenchbndr CLM

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    So let me get this straight,......

    The UPPER receiver's pin bosses will not fit into the LOWER receiver?

    Width of the inside of the lower receiver for fwd pin boss should be: .500" +.000/-.004"
    Width of the inside of the lower receiver for rear pin boss should be: .438 +.010/-.010"
     
    Last edited: Mar 5, 2010
  12. cliffb

    cliffb

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    I believe the fix is easy if it is what I think.

    Put a slight chamfer on the rear corners of the upper receiver rear pin block. Just a few strokes with a jeweller's file is all you need. Easily touched up with a black marker.

    Let me know if you need some pics.
     
  13. DesertEagle.45

    DesertEagle.45 USMC 8531 Lifetime Member

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    The lower reciever at both the takedown and pivot pin should have a slot cut to .500 +.000 -.004.
     
  14. emt1581

    emt1581 Curious Member

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    It actually fit just fine in one of the lowers so I didn't have to do any work.

    I also put the LPK together without instructions or tools...well pliers for the roll pins. BTW, on my trigger gaurds I can never get the roll pins in all the way, they stick out 2-3mm's...any ideas to get them into place all the way?

    Thanks!

    -Emt1581
     
  15. DesertEagle.45

    DesertEagle.45 USMC 8531 Lifetime Member

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    You need a pin punch. You could also try a small center punch the try and coax it in. Maybe a nail.
     
  16. harleyfx69

    harleyfx69

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    tap with hammer or crush with a press
     
  17. RMTactical

    RMTactical Battle Born CLM

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    That's a common problem. Probably just needs more elbow grease. Some can be a pain to fit together...
     
  18. harleyfx69

    harleyfx69

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    dont forget to support the ear of the trigger guard or youll be getting one of the magpul grips not by choice
     
  19. emt1581

    emt1581 Curious Member

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    It's got a MIAD grip already...not that I'm looking to break off part of the lower.

    -Emt1581
     
  20. thisaway

    thisaway

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    Have no fear! As long as the upper will fit into the lower, there should be no problems. In fact, a tight fit might help improve accuracy in some small way.