Pennsylvania Firearm Owners Association
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  1. #11
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    Default Re: Anyone lap the upper receiver on their AR builds?

    "...just because a part is precisely machined, doesn't mean it's going to be perfect in it's end use".

    A quote from George Orwell??
    There are two kinds of guns. Those I have acquired, and those I hope to.

  2. #12
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    Default Re: Anyone lap the upper receiver on their AR builds?

    I am assuming you think it is unwise to lap an ar upper, but I don't what to put words in your mouth. You comment like you have the experience to enlighten me. I would love to hear anything constructive you have to say......?


    I'll try again:

    Scope rings are milled by a machine that can probably measure in the ten thousandths of an inch. The weaver rail sections are milled by a machine that can measure in the ten thousandths of an inch. The receiver of the rifle is milled by a machine that can measure in the ten thousandths of an inch.

    And yet, the inaccuracies when assembling these parts are bad enough that a company makes lapping bars, and other companies make rings with inserts that are designed to accommodate for the rings alone not aligning with each other.

    Is is so hard to believe that a CNC machine that makes no reference off of the actual cylindrical cut inside the upper, could be off a thou or two on the face of where the barrel extension mates to it?

    Please feel free to either agree, or disagree, but at least bring something (more) to the discussion than snarky comments........
    Last edited by YBNORMAL; April 21st, 2020 at 09:10 PM.
    The smallest minority on earth is the individual. Those who deny individual rights cannot claim to be defenders of minorities.
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  3. #13
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    Default Re: Anyone lap the upper receiver on their AR builds?

    I accept, honor and credit your opinion(s). Please post the degree/percentage of accuracy (or other) improvement the procedure accomplishes after having performed it.
    There are two kinds of guns. Those I have acquired, and those I hope to.

  4. #14
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    Default Re: Anyone lap the upper receiver on their AR builds?

    Quote Originally Posted by YBNORMAL View Post

    That's a good question for an upper manufacturer. In fact, here is a video of an upper being machined and the receiver face is cut, and it appears to me that there is no perpendicular reference point for that cut other than the tooling, which can certainly have tolerance issues that stack.

    https://www.youtube.com/watch?v=ErrR6x-1RDo
    That video shows a billet upper being cut on a 5 axis machine with a single fixture. There is no tool tolerance, only the machine tolerance. It’s probably as accurate as the tool from Brownell's.

    Now machining a forging on conventional multi fixture tooling... that probably supports your position a little better.

  5. #15
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    Default Re: Anyone lap the upper receiver on their AR builds?

    Quote Originally Posted by Bang View Post
    I accept, honor and credit your opinion(s). Please post the degree/percentage of accuracy (or other) improvement the procedure accomplishes after having performed it.
    Well, if others are to be believed, they have found that doing it fixes their maxed out windage adjustment on their rear sights, with no other changes. So it stands to reason that some uppers are out of tolerance bad enough that it straightens the barrel enough to bring the iron sights back to center. I have never read of anyone that did it and their sights went "out" of room of adjustment.

    In my case, the linear comp and the handguard only have about 1/16 of clearance all the way around, so it would only take a thousandth or two at the face of the reciever to cause that misalignment 12 inches down the line. I haven't shot it yet to know where the sights are going to fall, so here we are, talking about guns and stuff. Isn't that what we are here for?

    Quote Originally Posted by imashooter2 View Post
    That video shows a billet upper being cut on a 5 axis machine with a single fixture. There is no tool tolerance, only the machine tolerance. It’s probably as accurate as the tool from Brownell's.

    Now machining a forging on conventional multi fixture tooling... that probably supports your position a little better.
    Could be, the accuracy of the turning of the table is the critical point I suppose.

    Let me put it to you this way, I used to run a very large (football field), very expensive (30 million dollar) commercial printing press. We printed high end catalogs, pottery barn, nieman marcus, white house black market, etc, etc. Precise, expensive customers, they wanted their models and product to look good. In addition to overseeing the entire press and it's 6 crewmembers doing their parts, I carried a magnification loupe in order to check registration and make moves to the different colors so that they registered properly to each other and the small white type wouldn't appear red, or cyan, or yellow. Imagine when you get a newspaper and it looks 3d, that's register, but newspaper printing is the lowest form of print quality there is, Automotive pamphlets that you get at the dealer to entice you to guy that shiny new car or boat are usually regarded as the highest. The moves that my press could hold and change were measured by .001.

    And as the Pressman, I used to repair this machinery as well. So long story short, the image for whatever we were running was shot onto a thin aluminum plate, and then wrapped around a steel cylinder and as the cylinder rolled, it picked up ink, then transferred it to a rubber blanket cylinder, then to the paper web. The machine that bent these plates (lead edge and tail edge bends) was extremely precise.

    But never the less, somebody not paying attention to an aluminum chip that falls in the wrong place, or a stepper motor that has a slightly worn bearing shaft, or a linear bearing that is wearing, or even the humidity being vastly different from the plateroom to the pressroom, would cause the bends to be out of parallel, or too short or too long, and then after only 20,000 impressions (one rotation of the plate cylinder is one impression, a plate should last a million imps before the image wears down). the plate won't properly fit to the cylinder, and would flex and crack, causing thousands of dollars in delay time and wasted product if nobody caught the crack. The press (can) run 3000 ft per minute, or 100,000 impressions per hour at top speed.

    Happened all the time.

    So forgive me if I don't blindly trust even very precise machines to guarantee that things are square.

    I have more of a "machinist" eye, than most, thank you very much
    The smallest minority on earth is the individual. Those who deny individual rights cannot claim to be defenders of minorities.
    Ayn Rand

  6. #16
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    Default Re: Anyone lap the upper receiver on their AR builds?

    I have lapped all of my uppers. It's not going to kill the rifle and its something that's only a few more extra minutes to do. I turn mine by hand though as I don't put em into a drill. I also bed the receivers which have a sloppy fit with the barrel extension.
    "A government big enough to give you everything you have, is also big enough to take it all away.
    Gerald Ford.

    Happiness is 5,000 rounds of match ammo.

  7. #17
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    Default Re: Anyone lap the upper receiver on their AR builds?

    By lapping , you wear away the thin anodized coating , and the bare aluminum can wear much faster.
    I don't speak English , I talk American!

  8. #18
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    Default Re: Anyone lap the upper receiver on their AR builds?

    Do we get apples and apples loads results thru lapped and non-lapped, showing the gain in repeatable accuracy? Assuming that is the goal?
    There are two kinds of guns. Those I have acquired, and those I hope to.

  9. #19
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    Default Re: Anyone lap the upper receiver on their AR builds?

    No.

  10. #20
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    Default Re: Anyone lap the upper receiver on their AR builds?

    Quote Originally Posted by abner13 View Post
    By lapping , you wear away the thin anodized coating , and the bare aluminum can wear much faster.
    I don*t see that area as a wear surface.

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