AR Upper Receiver Lapping Tool

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  • aclark

    Master
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    21   0   0
    Apr 22, 2009
    3,708
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    The 219
    Does anyone have one of these that I can borrow? Preferable around NWI, but if we can flat rate ship it I'd be willing to pay the $10 round trip. If you have a bit of compound (220 should do) that would be a great bonus. Looking to square up a couple of receivers in my safe, but don't think I need my own.

    PTG Upper Receiver Lapping Tool AR-15
     

    aclark

    Master
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    21   0   0
    Apr 22, 2009
    3,708
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    The 219
    The idea came into play after a lengthy thread on 6.5 Grendel and several PMs between myself and another respected member there. Will a non squared receiver outshoot my ability? Probably, but I have invested in several higher end components for this build, including a Lilja barrel so figured if I could borrow one of these to make sure the receiver face is squared, why not?

    Link to the thread.
    Longevity, Accuracy Tips for the AR15
     

    hondatech2k2

    Shooter
    Rating - 98.2%
    55   1   0
    Jul 10, 2011
    816
    18
    Greenwood
    Very interesting concept. I will add to the x3 that I have never heard of this process before. If you would, please post up your results with some pics so we can have a look see!! Good luck.
     

    ctbreitwieser

    Master
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    2   0   0
    Jun 14, 2011
    2,290
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    DuCo.
    Lapping the receiver would be pointless unless you trued up the locking lugs on the rear of the bolt and in the barrel extension, and also trued the bolt face. Even then I'm not so sure it'd really do anything beneficial. I'd also be concerned with removing too much of the hard anodizing an expose the soft aluminum underneath.
     

    aclark

    Master
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    21   0   0
    Apr 22, 2009
    3,708
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    The 219
    These were things that one of the other members suggested might be beneficial, and things that he does to his rifles as well as builds he does for other people.

    * Lapping upper receiver face to true.

    * Lapping bolt to barrel extension lugs (this creates an even distribution of the pressure load from the lugs to the extension)

    * Complete bolt work-over, polish face, de-edge extractor shelf, de-edge extractor, de-edge lugs if necessary, polish extension in critical quadrant.

    Again, don't know how much of this would be beneficial to me because my skills are minimal right now, but like I said....wanted to try and start somewhere. He also said that some companies square their receiver faces before anodizing and some are usually pretty close to square. Brands like AA do it before, and Aero Precision (what I have) are usually pretty square. Billet manufacturers are always square from his exp as well. (again, just going off what he said)
     

    IndyGunworks

    Grandmaster
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    25   0   0
    Feb 22, 2009
    12,832
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    Carthage IN
    lapping the bolt to the extension lugs might be the only thing in that post worth a damn.

    There are so many other things going on that as long as the receiver face is close to true your fine. the bolt is not solid with the bolt carrier and there is flex there. So even if the face of your receiver is not perfectly square as long as its not HORRIBLE, the bolt will compensate on its own. and as long as while compensating it has even contact all the way around it wont matter in the least.

    as for the last bullet point. that's a bunch of fancy talk. Find a piece of 600 grit paper, use something flat, paint stirrer or a file, or something similar and just go over anywhere on the bolt that's 90 degrees to anything else.

    There really is something to consider about taking off the hardest part of your receiver and exposing the soft aluminum under it. I really don't think the juice is worth the squeeze.
     

    fireball168

    Master
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    23   0   0
    Dec 16, 2008
    1,745
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    Clinton
    I've had one of the PTG lapping fixtures for several years.

    It is a perfect storm for me, Dave and his girls are pretty good at sales, and I like new tools.

    Far less than 20% show an uneven surface on the receiver face on the initial "cut".

    I use 320g silicon carbide. Polish off just enough to have 100% contact all the way around the ring, many times this does not break the anodizing. In the cases where it does break the anodizing, I would estimate the "ring" is less than .040" wide.

    Lapping the receiver would be pointless unless you trued up the locking lugs on the rear of the bolt and in the barrel extension, and also trued the bolt face.

    So even if the face of your receiver is not perfectly square as long as its not HORRIBLE, the bolt will compensate on its own.

    There really is something to consider about taking off the hardest part of your receiver and exposing the soft aluminum under it.


    The extension shoulder is the "recoil lug" to the upper receiver.

    There isn't any "compensating" for that.

    That soft aluminum is generally the same alloy that has been used for years in aluminum chassis rifle stocks, unanodized.


    A $20 tool, a few cents of lapping compound and a few minutes of time.

    It takes longer to clean up the receiver and tool afterwards.


    Is it worth it, who knows. Like surface grinding and lapping a bolt rifle recoil lug, I wouldn't do the job without doing it and it doesn't take long to do.
     

    churchmouse

    I still care....Really
    Emeritus
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    187   0   0
    Dec 7, 2011
    191,809
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    Speedway area
    I've had one of the PTG lapping fixtures for several years.

    It is a perfect storm for me, Dave and his girls are pretty good at sales, and I like new tools.

    Far less than 20% show an uneven surface on the receiver face on the initial "cut".

    I use 320g silicon carbide. Polish off just enough to have 100% contact all the way around the ring, many times this does not break the anodizing. In the cases where it does break the anodizing, I would estimate the "ring" is less than .040" wide.






    The extension shoulder is the "recoil lug" to the upper receiver.

    There isn't any "compensating" for that.

    That soft aluminum is generally the same alloy that has been used for years in aluminum chassis rifle stocks, unanodized.


    A $20 tool, a few cents of lapping compound and a few minutes of time.

    It takes longer to clean up the receiver and tool afterwards.


    Is it worth it, who knows. Like surface grinding and lapping a bolt rifle recoil lug, I wouldn't do the job without doing it and it doesn't take long to do.

    Folks used to say I took way to many steps building my race engines. Far to meticulous. Took blue printing to the extreme. They stopped saying that when they were looking at my taillights....:)

    Just saying, anything you do to square up a mechanism can not hurt.

    Beneficial....may be hard to gauge in a well blueprinted piece but every little positive thing done can add up to one very big positive. Just saying, its your time, use it wisely.
     

    Psode27

    Expert
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    4   0   0
    Jan 23, 2011
    1,234
    38
    Rochester
    Looks interesting! It seems to me that if you are using lower quality parts (60$ bulk uppers) that it might be more noticeable. I know with some of the billet uppers they claim crazy square/flat receivers, but I wonder if thats the case with my cheapo upper I bought on cyber monday....? I'd be curious. one of the reviews stated that you needed a lathe, is that completely true? Learn something new every day.
     

    hrearden

    Sharpshooter
    Rating - 100%
    4   0   0
    Feb 1, 2012
    682
    18
    Interesting concept. I can see the lugs affecting accuracy. The receiver I can see affecting function and evenness of wear.
     

    midget

    Master
    Rating - 100%
    6   0   0
    Apr 2, 2010
    1,619
    38
    Leo
    Helps ensure equal pressure of the barrel against the receiver. I don't see how it could do any harm. I've thought about buying the stuff to do it, but I am a perfectionist when it comes to things I build...
     

    chipdog4

    Sharpshooter
    Rating - 100%
    2   0   0
    Apr 2, 2008
    594
    34
    I remember reading a post (arfcom or snipershide) where Grendals were breaking lugs and they came to the conclusion that upper wasn't square and putting all the pressure on a couple of the lugs.

    I'll see if I can find it...
     
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