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Thread: X-Bolt Moderator Thread

  1. #1

    X-Bolt Moderator Thread

    I have just purchased a used browning x-bolt in .308 which is threaded 14 x 1

    The barrel dimensions are 15.33mm outer main barrel diameter, 13.90mm thread major diameter, 12.79mm thread minor diameter, 3.15mm Barrel thickness measured to outside thread, 12.54mm diameter between thread and shoulder (effective barrel thickness is approx 2.47mm)

    Looking for opinions on the following;

    1) The existing thread does not extend the full length of the cut and terminates 2.60mm from the shoulder. The diameter of this gap is less than the thread diameter but it is then stepped back up to thread diameter at the shoulder. Is there a reason for Browning not to thread it all the way?

    2) Is the current shoulder of 1.4mm sufficient for a moderator threaded 14x1 to butt up against without causing potential alignment issues or impact damage?

    3) I was considering having the barrel rethreaded to 1/2" UNF to match my existing moderators, which would appear to be possible given the existing dimensions. However this would reduce the effective barrel thickness to approx 1.75mm but provide a larger shoulder of 2.11mm. Is this barrel thickness reduction sensible on a light barrel .308, albeit it does seem to be a common thread size on other .308 rifles?

    Ultimately should I keep it 14x1 and buy a new moderator (or bridge) or have it rethreaded 1/2"UNF to match existing moderators?


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  2. #2
    Shame you don't live in Devon, i have a 30-06 X Bolt, i am selling the Wildcat mod shortly, nothing wrong with the mod, i just don't use them.
    Mine is 14x1
    Cheers
    Richard
    Last edited by devon deer stalker; 30-10-2015 at 19:49.

  3. #3
    You'll find that most threaded parts have an undercut at the shoulder - much easier to make it that way. The diameter of this undercut is very close to the root diameter of the thread. Many people have 1/2" threaded 30 cal rifles and have no issues whatsoever. Go ahead and get it threaded 1/2".

    The undercut may also be needed for the moderator to screw right back to the shoulder, depending on mod design.
    Last edited by takbok; 30-10-2015 at 19:12.

  4. #4
    Quote Originally Posted by takbok View Post
    You'll find that most threaded parts have an undercut at the shoulder - much easier to make it that way. The diameter of this undercut is very close to the root diameter of the thread. Many people have 1/2" threaded 30 cal rifles and have no issues whatsoever. Go ahead and get it threaded 1/2".

    The undercut may also be needed for the moderator to screw right back to the shoulder, depending on mod design.
    +1 - any thread cut on an item which could have any make of aftermarket reciprocal part placed on it up to the shoulder will have an undercut - this is to avoid the mating threads from becoming bound up before they meet at the perpendicular shoulder (particularly important with moderator threads).

    More than likely machine cut (but not always) - the undercut allows the thread cutting tool room to run into and withdraw during the machining process - avoiding contact with the shoulder...

    Ah, those were the days.......
    For Gods sake - don't tell her how much I've spent

    Ctrl-Alt FACT

  5. #5
    It is not the fact that it is undercut that appears a little strange. It is the stepped shoulder which appears unusual to me. One would normally have the shoulder in one plane to the full depth of the undercut.

    Providing there is a corresponding counter bore at the start of the thread on the moderator it will still come up snug to the main shoulder. What you do not want is for the female thread to hit the step before the shoulders meet.

    As it is second hand, can you find out if it was factory threaded? Can you compare it with others by Browning…maybe send them your photograph and ask if this is normal.

    Alan

  6. #6
    Quote Originally Posted by Alantoo View Post
    It is not the fact that it is undercut that appears a little strange. It is the stepped shoulder which appears unusual to me. One would normally have the shoulder in one plane to the full depth of the undercut.

    Providing there is a corresponding counter bore at the start of the thread on the moderator it will still come up snug to the main shoulder. What you do not want is for the female thread to hit the step before the shoulders meet.

    As it is second hand, can you find out if it was factory threaded? Can you compare it with others by Browning…maybe send them your photograph and ask if this is normal.

    Alan
    This has been factory threaded

    In comparison to my other rifles with aftermarket threads, they have an undercut that is at least half the size and there is no step in the shoulder. I don't have a 14x1 mod to check the fit but the more I look at it the more I think just get it re-threaded.

  7. #7
    Quote Originally Posted by huntsman81 View Post
    This has been factory threaded

    In comparison to my other rifles with aftermarket threads, they have an undercut that is at least half the size and there is no step in the shoulder. I don't have a 14x1 mod to check the fit but the more I look at it the more I think just get it re-threaded.
    I have only owned two Browning rifles, both threaded M14, both were threaded badly, same as yours.
    Last one I went with an M14 with spigot, worked very well, another option would be 1/2x28.


    Neil.

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  8. #8
    I have an ASE Utra SL5 on my factory threaded 6.5x55 X-bolt and it snugs up nicely on the thread and has no wobble. I have shot 20-30 rounds at the range through it without it loosening or affecting POI...

  9. #9
    I have threaded hundreds of barrels for mods, this is a poor example. If you can salvage the 14mm thread by having the shoulder squared and the undercut cleaned up(which should be no longer than 2mm) and the thread is a good fit,that would be the way to go.
    It would be better examined by someone who knows what they are doing to make sure all is good with concentricity etc.

    You ask about reducing the thread to 1/2" (unf x20)There is plenty of material to do this once the 14mm thread has been turned off,However, the maximum rifle bore for the 1/2" thread is 30cal, which leaves the wall thickness of the barrel only .064" (1.64mm). Not a lot between the o/d of the rifling and the i/d of the thread. With a .308 it will be .060". Hope this helps.jc

    PS I just seen your pic,I can only assume that the 'step' in the undercut is left for strength. A small radius would suffice, providing it is not stopping the mod from locating on the face of the shoulder.
    Last edited by Highlandsjohn; 27-11-2015 at 00:27.

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