Odd measurement request

Discussion in 'Black Rifle Forum' started by locknload223, Mar 13, 2010.

  1. locknload223

    locknload223

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    I need someone, preferably more than one person with a stripped lower to measure the depth of the tiny hole that houses the front take down pin retention spring. I say more than one person because I'd like to make sure I get the depth right and different brands may be a hair off.

    I have an HBAR Colt that has a threaded front take down pin and uses a screw on the left side to anchor the pin. I want to ditch the hokie screw and install a regular take down pin. Brownells was suppose to have a replacement for this and they sent me a pin that was 1/4" longer than the receiver with a detent ball also on the outside of the receiver. A very cheesy fix, would it work, yeah, but it's not correct. So I bought a standard front pin, detent pin and spring from my local shop and headed home. I take down the rifle to install said parts only to see there is no hole. I guess since Colt wasn't using that style of take down pin, they decided to skip drilling that hole.

    So, I can drill the hole myself but I need to know the correct depth so the spring has the correct tension on the detent pin. I guess the easiest way to measure would be to use a small enough drill bit and insert it, flat end first, mark it with tape, remove and measure.

    This would help me out alot and I would really appreciate it. Thanks a bunch if you can take the time.
     
  2. Alaskapopo

    Alaskapopo NRA ENDOWMENT

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    You should do that job with a drill press.
    Pat
     

  3. locknload223

    locknload223

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    Oh yeah, for sure. I have a small drill press and a Mill.
     
  4. GlockSupremacy

    GlockSupremacy Recycle Kids!

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    After checking two different brand unfinished lowers, the good news is you can screw it up!

    I am going to guess a quarter inch difference in depth between a doublestar lower and a superior lower.

    Here are the numbers:

    Doublestar (2x) .990" or 25.16 mm

    Superior 1.172" or 29.79 mm

    Bad news is wtf is "mil-spec"!?

    ETA: found the diagram finally, mil-spec is supposed to be 1.125"
     
    Last edited: Mar 14, 2010
  5. HAIL CAESAR

    HAIL CAESAR Senior Member

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    See what a few have been saying for a long time about all the "Me Too, we are Mil-Spec too!!!" companies.:rofl:
     
  6. locknload223

    locknload223

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    Thanks. The mil-spec measurement confirms with a blue print and tutorial someone provided me. Wish me luck.
     
  7. rkwrichard

    rkwrichard

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    Here is an additional graphic that might help.

    [​IMG]
     
  8. locknload223

    locknload223

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    Thanks. I wonder what that outter hole is for? Seems like it would just load up with dirt.
     
  9. rkwrichard

    rkwrichard

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    It is to put a drop of oil and also a drainage hole. Since most AR's are were designed and have been used around water the drainage hole is there so the water can escape and so pressure does not build up inside the blind hole.

    In some of the info I have been looking at it is called a breather hole used for venting the blind hole.
     
    Last edited: Mar 17, 2010
  10. locknload223

    locknload223

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    Got the hole drilled and the rifle back together, works great. Good times :supergrin:.

    SCARY!!
    [​IMG]
    [​IMG]