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Thread: Barrel detent for gas block set screw necessary?

  1. #31
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    Suwannee Tim --

    I appreciate your response. My intension is not to cut corners but to build a safe and reliable upper. I have a second upper in the works that will use a F-stamped FSB on a M4 carbine bbl purchased from BCM. I just got a look at the parts today and the only predrilled holes I saw in the FSB were for the gas tube (as expected). The tapered pin holes are absent but that's a project for another day. I don't know the tensile strength of those roll pins but I'm pretty sure the pin plus two set screws should hold the GB very securely. Again, not trying to cut corners. I order from McMaster all the time and may go for a grooved pin if the roll pin doesn't work out. But that's why I'm here asking questions Thanks again for your suggestion.

    -- ale

  2. #32
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    Progress report

    I had an hour before work today to at least add those dimples to the barrel under the GB. I clamped the workpiece using a pair of aluminum v-blocks and supported the breach end using step blocks. The transfer punch marks are barely visible but enough to find center along the x-axis. I used an edge finder to index off the y-axis.



    Rather than use an 11/64" drill bit, I just used a #5 combination Drill and Countersink cutter. I only needed to drill as deep as the beveled cutting edge. At this point its all eyeball...





    One down, move .450" along the x-axis and repeat...



    Test fit...perfect! I'll add the cross-pin before calling this project complete but at least it's progress



  3. #33
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    I am lost about the roll pin thing. The set screws are adequate if not bullet proof. The roll pin will neither be adequate nor bullet proof nor will it add to the reliability of the set screws. Maybe I misunderstood. Are you going to roll pin the set screws? Now that should hold!
    Last edited by Suwannee Tim; 01-15-13 at 18:35.

  4. #34
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    My BCM barrels have always come with one dimple. I always viewed it only as a means of orienting and holding the gas block in place so that it could be drilled and pinned accurately.

    I'm no machinist, but every gas block I've ever seen or had pinned by quality gunsmiths, Noveske, ADCO or Ranier, even though they had a set screw, was always done with a solid pin. I've never seen one done with a roll pin. I guess I'm a little skeptical.

  5. #35
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    Stake the screws and call it done.

  6. #36
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    I'm going to tool up for taper pin reaming this year. There's no getting around it... the Lo Pro gas block faggotry is here to stay... as much as it pains me.
    "You people have too much time on your hands." - scottryan

  7. #37
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    The problem with taper pins is some of the stainless gas blocks. They are too hard to cut without tearing up a lot of HSS taper reamers, while straight reamers are available in cobalt.

    A coiled roll pin has PLENTY of shear strength to hold a gas block in place.

  8. #38
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    Ooooh... good to know.
    "You people have too much time on your hands." - scottryan

  9. #39
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    Quote Originally Posted by Todd.K View Post
    The problem with taper pins is some of the stainless gas blocks. They are too hard to cut without tearing up a lot of HSS taper reamers, while straight reamers are available in cobalt.

    A coiled roll pin has PLENTY of shear strength to hold a gas block in place.
    Todd, are the pins that Noveske uses straight pins?

  10. #40
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    Quote Originally Posted by mtdawg169 View Post
    Todd, are the pins that Noveske uses straight pins?
    The Noveskes I've put together for guys have had straight pins. The fit great.
    "You people have too much time on your hands." - scottryan

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