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AR upper to lower mating

Discussion in 'Rifle Country' started by lencac, Dec 29, 2012.

  1. lencac

    lencac Well-Known Member

    Hi guys :neener:
    I'd like to get your thoughts on something. AR-15.
    Using a feeler gauge how much clearence between your upper and lower receiver is there :scrutiny:
    How much is acceptable :eek:
    thanks :)
  2. roklok

    roklok Well-Known Member

    As long as it functions properly, the clearance should not matter much. However, loose upper to lower fit bugs the hell out of me, so I glass bed my uppers to their respective lowers. End result is rock solid.
  3. gotigers

    gotigers Well-Known Member

  4. Revoliver

    Revoliver Well-Known Member

    This is a very good point to bring up as mine has a tightening screw in it as well and I often wonder if people miss noticing that as it's not often advertised on lower receivers (like mine, it was a very nice bonus to an awesome lower that I already loved but did not have this bonus feature advertised).

    Also, as for the 'wedge', you could just use a spare foam earplug for free instead of paying $6+.
  5. lencac

    lencac Well-Known Member

    Hi Guys:
    USING A FEELER GAUGE how much clerence do you have?
    When these forgings are machined on an EDM machine there is an "allowable" tolerences. Some say .010 in. and some say .015 in. I suppose it would depend on what kind of quality control at the machine shop is followed. So either way you can have a stack-up of tolerences.
    So with the intended bearing surfaces being the parting line of the upper and lower receivers, if the tolerences of the 2 receivers matched-up perfectly. But they never do, perfectly. If the rails of both receivers at the parting line are not in contact then the bearing surface will end up being where the pins go through. The further apart the upper and lower are the more "wobble", at the upper receiver pin loops will occur as the rifle gets shot, serviced, cleaned, banged and beat up. Yes :scrutiny:
    I have 3 ARs that have .003 in. clearence. I have 1 brand new AR, never shot, "matched" upper and lower receiver from the manufacturer. It has .013 in.
    So hence my question.
    How much clearence does your rifle have? :)
  6. k_dawg

    k_dawg Well-Known Member

    It is a pity that most uppers are not made a little overside, so you can custom fit it to your lower.

    My JP Rifle's upper was that way. With just some minor fitting, it is very solid, even without the pins being inserted.
  7. 1911Jeeper

    1911Jeeper Active Member

    Don't know and have never bothered to measure. Rifles shoot just fine. After a while, the wobble bugged me so I got some accurizing wedges to "fix" the wobble.

  8. lencac

    lencac Well-Known Member

    Apperently using a feeler gauge is a bit much.
    I was just looking for some measurements, not rhetorical.
    Thanks anyway. :rolleyes:
  9. MachIVshooter

    MachIVshooter Well-Known Member

    It varies. I've seen anywhere from 0.004" to 0.017", and the amount of upper/lower wobble had nothing to do with it.

    I think the market prefers a little slop with universal interchangeability to swiss-watch fitment of mated parts that are incompatible with others.

    I can't stand the wobble, so I shim the front pivot. This shim is cut from 0.010" stainless brake caliper hardware, and preloads a little when closed, which keeps everything tight:

  10. madcratebuilder

    madcratebuilder Well-Known Member

    Download a copy of the ARMY TM 9-1005-319-23&P. It well outline the testing procedure with feeler gauges. As I recall the max is .018-.020" area.
  11. hentown

    hentown Well-Known Member

    I'd suggest that any $$ contemplated for buying that feeler gauge be spent, instead, on a good supply of Paxil and a couple of years of psychotherapy for that OCD! :cool::eek:
  12. rhinoh

    rhinoh Well-Known Member

    Then maybe you should have left out the part in the OP asking for people's thoughts.:uhoh:
  13. lencac

    lencac Well-Known Member

    Oh,it's on now boyz :banghead:
    Rhinoh, the subject matter wasn't even addressed in the first replys :(
    Hentown, I AM NOT ODC :what:
    Now Madcreatebuilder is on to something. Wow, looking at what .013 in. looks like, .020 in. would be unacceptable :uhoh: .............. to me anyway :scrutiny:
    And I'm totally down with what MachIVshooter is layin down, if you're pickin up what I'm layin down? Using the brake hardware is ingenius :D Being a certified Master Ford technician for 28 years I can appreciate the resourcefulness.
    That also might explain the OCD :rolleyes:
    Last edited: Dec 30, 2012
  14. Robert

    Robert Moderator

    Play nice kids, or this will get locked.
  15. Grmlin

    Grmlin Well-Known Member

    MACHIVSHOOTER, got any extra spacers handy? I have a rubber wedge in mine and don't care for it. The slop in my M&P seems to come from the front pin area
  16. proud2deviate

    proud2deviate Well-Known Member

    I just stuck a gauge in my Windham SRC, and came up with .006"
  17. Cosmoline

    Cosmoline Well-Known Member

    Is it possible for poor fit (too large a gap) to cause problems with the bolt stop? I've been wondering about that with the issue.
  18. gotigers

    gotigers Well-Known Member

    That is a nice fix, MachIV.
  19. MachIVshooter

    MachIVshooter Well-Known Member

    That'd have to be a pretty darn big gap.
  20. Nasty

    Nasty Well-Known Member

    I was the Base Weapon Inspector for many years...routinely checked for any over .020

    Most very very loose, few ever went beyond .020

    In an automatic, generous tolerances are usually a good thing for reliability/function.

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