Adding a tensioning screw to AR receiver
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Thread: Adding a tensioning screw to AR receiver

  1. #1
    Chief Administrator 7.62x39's Avatar
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    Default Adding a tensioning screw to AR receiver

    While I do not think that this is necessary for a properly machined lower, I have had folks ask me about them so I figured I'd post this.

    I set the mill up like this, using the following datum points. The normal "Y" axis zero, the flat area just behind the PG mounting boss for the "Z" zero and .156 (half of 5/16") to the right of it as the "X" zero.





    Using a 5/16" end mill I machined along the X axis .265 to the left into PG mounting boss. You do not need to mess with either the Y or Z just leave them locked.







    Drilled it out with a #3 bit.





    Tapped it to 1/4"-28





    Added 1/4"-28 X 3/4" set screw. It sits well below flush when fully installed

    .

  2. #2
    Gunco Veteran perry's Avatar
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    I hate to ask this but what is the purpose of it?

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    No Hope For Me 1biggun's Avatar
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    So the upper fits tight and dosent flop around killing accuracy and wearing pin holes out

    My only concern is how fast will that screw wear into the upper?

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    NoWorkCamp4Me railbuggy's Avatar
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    Takes the wiggle out of a miss matched upper and lower. In my opinion a feel good thing. I can't see it helping score higher on paper.
    I prefer a tight fit with no air gap with upper and lowers. The gap in my mismatched Anderson lower Sota Arms upper I can slide a strip of 20 weight printer paper thru.

    Sorry Biggun. I type slow.
    SOON-We already lost the war. You are the resistance.

  6. #5
    No Hope For Me 1biggun's Avatar
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    I doubt any loose part helps accuracy.
    Hammer swing and hitting the firing pin alone can move a loose upper.
    Various harmonic changes from Wichita way the upper is resting can't help.

    I have never seen a super accurate AR with a loose upper.

    Many guys only need minute of man so it won't matter.

    I note many down play this issue . It's often the same guys who will insist on a free float tube and a high end optic and then shoot Wolf ammo.

  7. #6
    gunco irregular moleman's Avatar
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    I remember seeing an article on the Military shooting teams and mods to their rifles. They did the same thing basically by bedding the rear takedown lug while keeping the action open a couple thousands with a feeler gauge.

  8. #7
    No Hope For Me 1biggun's Avatar
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    The military teams do quiet a bit to there gun.
    Different twist rates,chambers,and custom barrels.

    Part of the whole M16 is so accurate myth.

    A lot can be learned from there work.

  9. #8
    Gunco Veteran perry's Avatar
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    and to think we use to pile c rats match books cin them to get the radle out.

  10. #9
    Chief Administrator 7.62x39's Avatar
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    Quote Originally Posted by 1biggun View Post
    My only concern is how fast will that screw wear into the upper?

    UPPER RECEIVER TENSIONING SCREW FOR AR15 RECEIVER by: Buckley QC
    .

  11. #10
    Gunco Good ole boy kernelkrink's Avatar
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    So what's wrong with using the little $1 rubber wedgie thingy?

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