Roll pin as barrel pin? ??

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  • Goodcat

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    So here I am with my final 4.5” barrel choice to put my SBR back together, because I got the wrong threads on my first one and I don’t feel comfortable with the thread adapter... comes in, go to install, and instead of the usual barrel pin, I see a roll pin bigger than the receiver spot. What the heck am I looking at? Maybe one of those things that’s common I just haven’t run across.

    edit, tapped right in with tiny pressure from rubber mallet, but my question remains!

    edit #2 Speed fun video after done!

    [video=youtube_share;1jooMHB2_-M]https://youtu.be/1jooMHB2_-M[/video]
     

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    Goodcat

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    Anddddd she’s done again!

    edit. Pic redo for right side up.
     

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    AllenM

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    That's a new one on me. I'm sure it will be fine though.

    Gun looks great. Too bad you put it together upside down
     

    Goodcat

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    AllenM, I was suspended upside down while assembling. :/ If YOU haven’t seen one, they must be rare!! Wild.

    the brand name is match precision, eBay barrel for cheap. I’ll see how she runs today
     

    nrgrams

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    Seeing a roll pin for a barrel pin is a first for me, but I've only done a handful of builds myself. But if AllenM says it's good to go, my mind would be at ease. The build looks great and let us know how it runs!
     

    1911ly

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    The pin is an alignment pin right? The barrel nut holds it (barrel). It should be fine. I agree with Allen. If I had nothing else I would roll with it.
     

    Goodcat

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    Seeing a roll pin for a barrel pin is a first for me, but I've only done a handful of builds myself. But if AllenM says it's good to go, my mind would be at ease. The build looks great and let us know how it runs![/QUOTE]

    She runs FAST! Here’s a vid, updating original post with it too. Too fun.

    [video=youtube_share;1jooMHB2_-M]https://youtu.be/1jooMHB2_-M[/video]
     

    AllenM

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    I was searching for a barrel online yesterday for a pics build and one of them showed a roll pin in the pic too. It was a taccom,
     

    sloughfoot

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    I graduated from Minneapolis Vocational High school in 1969 as a machinist after studying and working with a variety of machine tools for 4 years. I never worked a day since as a paid machinist but have spent many hours in machine shops building prototypes and various housings for other things I was creating. I am not a professional machinist. I have built things under the direction of some very good machinists. I do not claim to even be close to a pro's expertise.

    End of disclaimer.

    However, I remember distinctly being told by many more knowledgeable than me, that roll pins are not appropriate as locator pins for dissimilar metals. To locate a steel part to an aluminum part requires a solid steel round pin. A roll pin is simply not appropriate for this function. The cost is the same.

    But I am not the standards police and ultimately I don't care what standards you use to build your rifle. Just as long as you don't sell it to me with a roll pin locating the steel barrel extension to the aluminum upper receiver.

    Thank You.
     
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    praff

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    I know this thread is a little long in the tooth, but I thought I would share what I have done in the past with a sheared pin from someone trying to remove a muzzle device. The only axial load that this pin is ever gonna see is the load of the bullet leaving the barrel and imparting a twisting force (cant be much with a tight barrel nut), and maybe the force from installing and removing a QD suppressor. It is probably fine, but it is so cheap and easy to replace, why not just put a piece of drill rod in there. Two minutes with a cutoff wheel and a belt sander and it is done.
     

    duffman0286

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    That's a new one on me. I'm sure it will be fine though.

    Gun looks great. Too bad you put it together upside down
    Roll pins are stronger than people give them credit. My UMP .40 was this way if you remember and the barrel is designed to be easily removed in a UMP by hand... That's just the way HK designed them and a blow back is a pretty violent action
     

    Goodcat

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    About 250 rounds down so far and no issues. Having accuracy issues with tirant 9mm with fixed barrel spacer 4 moa at 25 yards without. Gotta send my can setup in!
     

    engineerpower

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    However, I remember distinctly being told by many more knowledgeable than me, that roll pins are not appropriate as locator pins for dissimilar metals. To locate a steel part to an aluminum part requires a solid steel round pin. A roll pin is simply not appropriate for this function.

    Who ever told you that was talking about either galvanic corrosion, or stress forcing the harder object to deform the softer object. A sufficiently sized pin doesn't need to be solid if it was bear the expected load.

    Mechanical Engineer here who owns a machine shop; the roll pin will be just fine. It's simply for aligning the barrel around a single axis of rotation; all the load is born in the barrel nut and receiver threads. The gun would run just fine without the pin, and as long as you didn't mount it t0o far off the gas tube would still enter the upper.
     
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