.5x28tpi threaded length.

Discussion in 'Weapons' started by Fallschirmjäger, Jan 15, 2020.

  1. Fallschirmjäger

    Fallschirmjäger I watch the watchers

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    Anyone happen to know the standard length of the threaded portion of a barrel threaded at .5 diameter and 28 threads per inch?
    I'm having the barrel of my Bushmaster M17S shortened to a minimum and want to convert to a standard threaded length and the extra length used by Bushmaster. (Yes, I could say 'just thread it to standard', but I'm also doing this in CAD and am being picky about my little hobby drawing).
    I'm kinda hoping for something like this by the time I'm finished, although this doesn't reflect the Picatinny rails or M-Lock mounting points I'm putting in the drawing.
    The problem is that I am going to need to retain either a short section of the barrel shroud or cut the receiver to a bit longer than I want in order to meet the 26" OAL length, so I'm playing around with various configurations.

    [​IMG]
     
  2. 175FO

    175FO Member

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    Here you go
     

    Attached Files:


  3. Nemo

    Nemo Man of Myth and Legend

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    If I am reading that diagram right, its less than 1/4 inch of threads to attach to. That seems awful short to me. I think at least half inch would be proper.

    Nemo
     
  4. 175FO

    175FO Member

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    a little over half an inch.
     
  5. Nemo

    Nemo Man of Myth and Legend

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    So is the red dX 0.22in or blue dZ 0.565in the length of threads? It appears to me the lines show the dX (horizontal in pic) is thread length and dZ (verticle in pic) is diameter?.

    Although it appearing to be properly scaled conflicts that view.

    Nemo
     
  6. gunsmoker

    gunsmoker Lawyer and Gun Activist

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    1E331AFD-23EF-4336-AA13-7BAC97A37F68.jpeg B2BD1E1D-E117-4485-952C-07DCA33D4435.jpeg 7297D086-435D-4B15-BAA3-96565E418687.jpeg This Green Mountain Ruger rifle barrel was threaded by gunsmith Burrell Sullivan of Sullivan's classic arms in downtown Cumming about 15 years ago. He knew that my intended use was a rimfire suppressor, a silencer. But I told him I wanted to be free to use a variety of other muzzle accessories on it --whatever was threaded 1/2" x 28 turns per inch.

    For anyone having trouble seeing the pics, the threaded section is .358" or 9.1 mm.

    Note there is an undercut area which creates a little gap between the last thread closest to the muscle and the flat face of the turned gun barrel itself.
    I can't Measure that gap with the tool I have, but I would estimate it to be the thickness of a little more than one, but less than two, turns of threads. Meaning more than 1/28 of an inch but less than 1/14 inch.
     
  7. gunsmoker

    gunsmoker Lawyer and Gun Activist

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    AC0D64E4-356C-46C7-B9DF-D63A06B1A9D7.jpeg A76E0EA1-3763-4E61-8C05-63C3FAFC7282.jpeg

    This Browning Buck Mark barrel was threaded by gunsmith Andy Gazaway of Cumming, maybe 7 or 8 years ago.

    He also knew my purpose was to use a rimfire silencer, and AAC Pilot. And other muzzle accessories, to include fake suppressors, flash hiders or muzzle compensators.

    The threaded section is a little shorter --only 34/100 of an inch (8.65 mm)
    and it seems to have a larger gap in between the last thread and the flat face of the pistol barrel.
     
  8. gunsmoker

    gunsmoker Lawyer and Gun Activist

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    Well, according to this website of suppressor manufacturer Thunder Beast Arms, 1/2" x 28 T.P.I. threading is *not* the same for centerfire rifle muzzles as it is for rimfire guns like my .22lr barrels pictured above.

    My threaded section should be nominally .40 of an inch, minus the cutout or recess between the last thread and the face of the barrel.

    Any centerfire rifle or carbine threaded 1/2 x 28 should have a threaded section that is .60" long (again, minus a few thousandths for that extra deep unthreaded groove.)

    https://thunderbeastarms.com/tech/thread-specifications
     
  9. 175FO

    175FO Member

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    .565 is the length of the thread.
     
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  10. Nemo

    Nemo Man of Myth and Legend

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    Those points on the other side of you caliper won't fit in there and give you a measurement?

    I have used mine for similar measurements and obtained good results.

    Nemo
     
  11. Nemo

    Nemo Man of Myth and Legend

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    Maybe I need to reread the reading diagrams chapter.

    Nemo