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Thread: "Truing" an AR's receiver face?

  1. #91
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    Thanks for the detail on the process for chamber and threading, I have never seen it done from start to finish online. There's a ton of bolt gun cambering videos, but little to none on the AR's just lot's of barrel threading links.
    Any barrel especially a custom high dollar barrel, one would expect only the closest attention to detail in the chambering process. We have seen some scary videos of VERY sloppy uppers and folks gobbing on the blue loctite.
    Maybe just start over? To each his own I guess. When I start a lap I work it by hand for about 30 seconds then check it, if I see a half moon I continue. I lap only until I have a full visible circle, then I stop.

    Thoughts on the bared aluminum after lapping? Dissimilar metals, electrolysis or corrosion at the flange contact points? Are most barrel extensions used also coated or hard chrome treated?
    Last edited by smihtp; 01-22-16 at 13:57.

  2. #92
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    I'm curious why the face is off .002" if it's all done in one op, besides shitty fixturing? If I was out 2 thou over an inch on the same op they'd be all over our Makino.

  3. #93
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    So, if one DID want to bed a loose extension into an upper, what exact type of blue loctite would one use?

  4. #94
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    While the above method listed is popular in use, it is "a" method and not "the" method used by all. There are "pro's" and "con's" with each. The above mentioned method is one way to "skin the cat", there are others done, circa up to 2010 at least.

  5. #95
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    Quote Originally Posted by BSmith View Post
    I'm curious why the face is off .002" if it's all done in one op, besides shitty fixturing? If I was out 2 thou over an inch on the same op they'd be all over our Makino.
    .002 and you start kicking parts? What are your repeatability requirements? Are you making AR receivers?

    Had no idea they would be that tight.


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  6. #96
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    Quote Originally Posted by BSmith View Post
    I'm curious why the face is off .002" if it's all done in one op, besides shitty fixturing? If I was out 2 thou over an inch on the same op they'd be all over our Makino.
    You would need to ask the guys in quality control with the company making the receivers that one. All I can say is very few are square. The good thing is, if the extensions are tight in the bore it doesn't matter much.
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  7. #97
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    Quote Originally Posted by Brahmzy View Post
    So, if one DID want to bed a loose extension into an upper, what exact type of blue loctite would one use?
    It's just something to make the connection more rigid...take up space to keep the extension from moving in the receiver. Plain old blue works fine. When it comes time to remove the barrel stick a 3/4" wood dowel in the rear of the receiver and tap the barrel out. Blue does not really adhere to the anodizing.
    JMO- The barrel to receiver connection is crucial for accuracy because it connects the scope to the barrel. It's the same reason many are making bolt gun actions with integral scope rails and recoil lugs.
    AR15performance
    TRUMP 2020
    The 6.8 is the best choice for hunting deer and hogs with an AR15.

  8. #98
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    While I love MEGAs stuff and own heaps of it, one of their MATEN series 308 uppers is not as tight fitting as I'd like, in fact not even close. I think in general 308 parts are tougher to fit as there's just so many variables without as many standards.
    I think I will try the bed thing as this new MATEN upper is loose as a goose with 2 of my 308 barrels. So strange as I bought one of the first MATEN uppers / lowers that came out of MEGA and I had to put the barrel in the freezer AND heat gun the upper just to get them together. This new one is ridiculously loose.
    Last edited by Brahmzy; 01-23-16 at 11:15.

  9. #99
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    Quote Originally Posted by JC5188 View Post
    .002 and you start kicking parts? What are your repeatability requirements? Are you making AR receivers?

    Had no idea they would be that tight.


    Sent from my iPhone using Tapatalk

    No, we do mold work. But if you are machining aluminum .002" out of square over an inch when the machine is square within 80 millionths over the entire travel... With it being done on the same op, you should be a LOT more square than .002 over 1".

    I know, there's a tolerance, and if you hit nominal within a couple tenths (ten thousandths of an inch) every time when the part only needs +-.002 then you're wasting time. But, this is a squareness issue on a setup that is inherently square.

    FWIW, I can indicate a 15" part that was hard milled (52-54 HRC), and the perpendicular side is cut 4" down and see no more than .00003" total movement on the indicator and not uncommon to see it within .0001". All that is cut in one op. Deck the top, mill the sides.

  10. #100
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    Quote Originally Posted by constructor View Post
    You would need to ask the guys in quality control with the company making the receivers that one. All I can say is very few are square. The good thing is, if the extensions are tight in the bore it doesn't matter much.
    Please don't take that as me questioning you. There's no dispute that they are machined that way.

    It also amazing that, whoever in the other thread, is making lowers that are as off center as they are. But at least that's different setups.

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