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Thread: Thread size & barrel diameter

  1. #1

    Thread size & barrel diameter

    Hi all


    Just looking for some advice from the more experienced:

    I am getting a heavy barrel CZ thread cut, and the moderator i am looking at is threaded 1/2 UNF.

    So here's my question: Is it advisable to thread cut a heavy barrel to this or should I be looking at M18x1 etc

    Would appreciate your advice

    Thanks

  2. #2
    Quote Originally Posted by Look deer View Post
    Is it advisable to thread cut a heavy barrel to this or should I be looking at M18x1 etc
    Some people would do this, perhaps because they already have a moderator with this thread, or want to standardise on the same thread as other rifles already owned.

    But if you are starting from scratch, much better to use a larger thread.

    5/8 UNF is the larger common imperial thread. M14x1, M15x1 and M18x1 are often found. M14x1 is pretty standard on Tikka, Sako etc.

    The finer pitch of the metric threads mean they are less likely to loosen, and less metal is cut away in the thread.

    Don't over-do it though, there needs to be a decent (and well cut) shoulder for the moderator to line up on.

    Also consider using a spigotted thread, which is the technically superior method, though not particularly common. M17x1 spigotted is pretty much the standard.

    If it is .30 calibre I'd never do it, because there would be hardly any metal left between the bottom of the thread and the rifle bore. About 50/1000" if I've got my sums right, assuming the thread is cut perfectly central to the bore.

    There is also the possibility that any internal stress in the barrel could cause the threaded portion to swell when so much metal is cut away, which would do nothing for accuracy. CZ use hammer forged barrels which have the highest internal stresses.
    Last edited by Sharpie; 18-03-2013 at 14:23.

  3. #3
    My cz varmint 22lr is threaded 1/2 unf and it performs well.
    I was told all rimfire moderators came with this thread but I dont know if this is true or not.

  4. #4
    Quote Originally Posted by palo View Post
    My cz varmint 22lr is threaded 1/2 unf and it performs well.
    I was told all rimfire moderators came with this thread but I dont know if this is true or not.
    You are quite right, if this is a rimfire then 1/2" x20 UNF would be the standard thread and is the sensible one to use. I was talking about centrefire rifles where the decision is more complicated.

  5. #5
    [QUOTE=Sharpie;546421]

    Also consider using a spigotted thread, which is the technically superior method, though not particularly common. M17x1 spigotted is pretty much the standard.


    Agreed, I would definitely go with a spigot.


    For what it's worth, all my sporter profiles are M14 spigot. I don't have any heavy barreled rifles.

    Kind regards,

    Tim

  6. #6
    I see 1/2" UNF threads on a lot of .30-cal rifles

    Makes about as much sense as an ashtray on a motorbike


    I had my heavy barrel .223 threaded 9/16 x 24...as that was the largest dia. thread the factory could do at the time...


    1/2" UNF is the thing for .22lr bunny guns - anything else =

  7. #7
    I have a:
    .17M2
    .17HMR
    .22WMR
    .22LR
    .222Rem
    .243Win

    all sporting barrels, all threaded 1/2" UNF

    ​plenty of meat on the bore end of the .243

  8. #8
    [QUOTE=Tim1;546527]
    Quote Originally Posted by Sharpie View Post

    Also consider using a spigotted thread, which is the technically superior method, though not particularly common. M17x1 spigotted is pretty much the standard.


    Agreed, I would definitely go with a spigot.


    For what it's worth, all my sporter profiles are M14 spigot. I don't have any heavy barreled rifles.

    Kind regards,

    Tim
    Tim spigotted is definitely superior but you also have to have the corressponding counterbored mod, not all mods are machined for spigotted installations.

    Ian.

  9. #9
    what is "spiggoted"?

    I was thinking it is the non threaded part between thread and barrel. but this description doesn't fit my mental picture

  10. #10
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    Quote Originally Posted by bewsher500 View Post
    what is "spiggoted"?

    I was thinking it is the non threaded part between thread and barrel. but this description doesn't fit my mental picture
    The one on the left is, I think... sorry the pic's not brilliant.

    Attachment 26075

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