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AR upper to lower mating

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

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  1. lencac

    lencac Member

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    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 Member

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    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 Member

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  4. Revoliver

    Revoliver Member

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    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 Member

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    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 Member

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    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 Member

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    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 Member

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

    MachIVshooter Member

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    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:

    ARShim.jpg
     
  10. madcratebuilder

    madcratebuilder Member

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    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 Member

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    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 Member

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

    lencac Member

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    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 Staff Member

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

    Grmlin Member

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    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 Member

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

    Cosmoline Member

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    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 Member

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    That is a nice fix, MachIV.
     
  19. MachIVshooter

    MachIVshooter Member

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

    Nasty Member

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    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.
     
  21. Reloadron
    • Contributing Member

    Reloadron Member

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    The following quote is taken from The New Competitive AR 15 written by Glen D. Zediker. It has some bearing on the subject of this thread and more information.


    The author makes some excellent points as to the fit of upper to lower and how this fit overall effects the accuracy of the rifle. The book is well illustrated and the quote represents a few pages of the total 470 pages.

    Another excellent book is Black Magic The Ultra Accurate AR 15 by John Feamster.

    Considering the cost of a good AR 15 rifle I find it unusual that many people will not invest a few dollars in a good book or two. While every book out there should not be considered gospel the books written by well accomplished shooters should always be considered.

    Ron
     
  22. lencac

    lencac Member

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    Very good write-up. I would tend to agree.
    There is no way that when the barreled upper can slightly move independent of the held lower receiver, wether or not off the bench or some other, there's no way it will be as accurate as being a solid fit. This for obvious reasons. Wobble definitely detracts from the rifle's overall appeal.
    I suppose too the less the upper and lower are taken apart the better.
    The rub here is I always clean the barrel from the breech end.
    To a small degree also a .003 in. gap would far better resist forgeign material getting into the receivers than a .020 in. gap.

    I recently was sent an upper and lower by a manufacturer as a Christmas gift. I do business with them through a second non-firearm related business.
    So the owner said he had the two receivers made as a matched pair. I said what does that mean? He said that both upper and lower were mated for lengthwise alignment and then the take-down pin holes were line-bored together and the width of the take-down pin locations were machined so as to require an almost press fit as the upper pin holes slide down into the lower receiver. Super tight and perfect fit and when all put together the two feel as one. However, it does have a .013 in. gap through the entire length of the receivers. The other two I have are in the .003-.004 in. range.
    So I like the shim idea. Perhaps both front and rear.


    So hence my curiosity :scrutiny:
     

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  23. HOOfan_1

    HOOfan_1 Member

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    I don't have a feeler gauge, but my Daniel Defense upper fits my Armalite lower so tightly, that it is a chore to push out the takedown pins.

    I've had it for about 8 months now, and have probably had them apart about 30 times, but it is still a tight fit.
     
  24. Reloadron
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    Reloadron Member

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    From the article I posted "Keep both pins greased. Heavily". So do you grease the pins? With a rifle that tight (not necessarily a bad thing) every time the rifle is fired there is tension changing between the upper and lower. The pins are made of steel and the upper & lower holes are drilled in aluminum. Slowly something will begin to give and I do not see the pins giving. This leads to the possibility of the holes the pins rest in becoming elongated. That being a bad thing. If this rifle is as tight as you say I doubt you could manage to get the blade of a feeler gauge in there. Grease the pins would be my suggestion.

    Ron
     
  25. HOOfan_1

    HOOfan_1 Member

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    I usually put some Ballistol on the pins
     
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