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Thread: Vertical line on upper receiver

  1. #11
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    While the reference point ( datum )for machining seems plausible, I don't think that is what it is for. A datum would be a point ( Vertex ) not a line. the inside corner at the pistol grip attachment point would be a great datum point. The notion that it may be an index point or tab for a machining fixture doesn't seem right either, the mark is too small to be precisely placed into a notch and not close enough to an edge to be accurately lined up with a corresponding mark on a fixture. And as for a casting mark, why would that particular casting mark be left on the piece when great care is taken to remove all of the others? And why would that mark be left on ALL of the uppers that are made no matter who they are made by?

    Vince
    Last edited by EW1066; 07-16-10 at 23:48.
    When injustice becomes law, rebellion becomes duty. Thomas Jefferson


  2. #12
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    I'm gonna call around to a few forges Monday if we haven't gotten an answer yet.

  3. #13
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    it's a reference mark for the M203 Quadrent Sight.

  4. #14
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    Quote Originally Posted by 10lrrp View Post
    it's a reference mark for the M203 Quadrent Sight.
    This?



    How is the reference mark used?

  5. #15
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    Quote Originally Posted by organdonor View Post
    This?



    How is the reference mark used?
    If the range quadrant (angular scale) on the sighting system moves up and down I would tend to go with this answer. However, looking at the above illustration, it appears to me that the sight arm travels up and down along the range quadrant. Which stands to reason considering the high launch angles used to launch a granade. If on the other hand it is used in order to consistently line up the bottom line on the quadrant so that sighting remains the same from gun to gun.....that would make some sense.

    Vince
    Last edited by EW1066; 07-17-10 at 14:04.
    When injustice becomes law, rebellion becomes duty. Thomas Jefferson


  6. #16
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    I just found this picture. Based on this picture it would be difficult to associate the mark on the receiver with the range quadrant on the m203 grenade sighting system.






    Vince
    When injustice becomes law, rebellion becomes duty. Thomas Jefferson


  7. #17
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    bump.......
    When injustice becomes law, rebellion becomes duty. Thomas Jefferson


  8. #18
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    I honestly never wondered what it was for, but now I'm curious?

  9. #19
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    Okay, I contacted the oracle, this is what the had to say...

    Colt used this vertical line, along with a "+" seen on early lowers (SP1, M1601), as a visual aligning mark used in the manufacturing process.

    While keeping in mind that this was all done using 50's era machining processes, the machinist would align the mark in a small viewing area before securing the receiver forging and cutting away.

    http://imageevent.com/willyp/firearm...=0&y=0&z=9&l=0
    Last edited by MisterWilson; 07-19-10 at 12:00.
    The Revolution will not be televised.

  10. #20
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    So it serves no purpose today

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