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Thread: Spigot or not to Spigot ?

  1. #1

    Spigot or not to Spigot ?

    I've had a number of different moderators on standard and heavy barrels but so far none have been fitted with a spigot. I will be specifying what I want when I get a new rifle so I will have the option. Spigot or not? If you have smithing experience in this area I would be grateful for your advice!

  2. #2
    Personally I like the spigot fitting not had any problems to date
    regards pete

  3. #3
    The spigot fitting is the superior method.

    The moderator is located in line with the barrel by both the spigot and the shoulder.

    With a spigot fitting the shoulder is 30 mm behind the muzzle. With a none-spigot thread it is only 15mm behind. Even ignoring the alignment due to the spigot this means the spigot fitting will be aligned at least twice as accurately as an ordinary thread.

    Even if the moderator comes loose, the spigot will keep it in line. With an ordinary thread it won't.

    With an ordinary thread much of the repeatability of alignment is down to how closely the thread on the barrel and the thread in the moderator are toleranced.

    With a spigot fitting this is almost a non-issue. Indeed the barrel thread can be made purposely loose to ensure interchangeability and avoid seizing etc.


    In practice what this means is that the spigot fitting is less likely to cause zero shift as the moderator is removed and replaced, as it should be every outing.

    If you have the option, choose a spigot. M17x1 spigotted is pretty much a standard for tactical applications.

    Comparison drawings of typical threads are here: http://jacksonrifles.com/zz-silencer...-t4-manual.pdf and here Maintenance

    A quick glance should show you the important differences.

    If you do choose a spigot, also get your 'smith to make a spigot diameter collar 18.5mm long. This would enable you to also fit a moderator with a none-spigot thread if you wished, keeping all your options open.

    PS: With a spigot thread it will take about nine turns to screw on your mod. With an ordinary thread 15 turns. Which may seem trivial, but worth considering.
    Last edited by Sharpie; 21-03-2014 at 23:22. Reason: the PS.

  4. #4
    My new custom .223 AI has got a spigot, it is as earlier stated the superiour method and just makes engineering sense.

    Steve.

  5. #5
    Makes sense to me too. If the foresight was being re-tapped to accommodate a moderator it would have to be even further back for the spigot wouldn't it. It might start to look odd.

  6. #6
    Quote Originally Posted by Sharpie View Post
    The spigot fitting is the superior method.

    The moderator is located in line with the barrel by both the spigot and the shoulder.

    With a spigot fitting the shoulder is 30 mm behind the muzzle. With a none-spigot thread it is only 15mm behind. Even ignoring the alignment due to the spigot this means the spigot fitting will be aligned at least twice as accurately as an ordinary thread.

    Even if the moderator comes loose, the spigot will keep it in line. With an ordinary thread it won't.

    .With an ordinary thread much of the repeatability of alignment is down to how closely the thread on the barrel and the thread in the moderator are toleranced

    With a spigot fitting this is almost a non-issue. Indeed the barrel thread can be made purposely loose to ensure interchangeability and avoid seizing etc.


    In practice what this means is that the spigot fitting is less likely to cause zero shift as the moderator is removed and replaced, as it should be every outing.

    If you have the option, choose a spigot. M17x1 spigotted is pretty much a standard for tactical applications.

    Comparison drawings of typical threads are here: http://jacksonrifles.com/zz-silencer...-t4-manual.pdf and here Maintenance

    A quick glance should show you the important differences.

    If you do choose a spigot, also get your 'smith to make a spigot diameter collar 18.5mm long. This would enable you to also fit a moderator with a none-spigot thread if you wished, keeping all your options open.

    PS: With a spigot thread it will take about nine turns to screw on your mod. With an ordinary thread 15 turns. Which may seem trivial, but worth considering.

    The threads should never be used for alignment. It is the shoulder to shoulder contact which should ensure barrel to mod bore alignment.

  7. #7
    I have just had my .223 A-bolt threaded and went with an M14 spigot, biggest possible thread on a slim barrel.
    Works great and much stronger than a standard thread when using a muzzle can.
    My little CZ527 in 7.62x39 is in being done now, again with an M14 spigot.
    As somebody mentioned, yes it starts to look a bit funny with the fore sight set back that far, so the sight is going
    on the thread protector, lets just hope if I ever need to pull the QD scope off for a some reason I have the fore sight in my pocket. Lol

    Neil.

  8. #8
    if the thread and shoulder are machined concentric and square to the bore respectively, and the thread is cut to within a thou clearance, then there is no need for a spiggot. it won't do any harm and has some merit for people who can't machine to benchrest tolerances or like loose fitting threads, but it is certainly not necessary for people who can. i wouldn't worry about which way it was done. none of my rifles have a spiggot, and moderators are still inline, even if loose by a turn or 2.

    it is true that it is the shoulder being square to the bore that gives a true allignment, but i'd rather my threads were snug to ensure maximum bearing surface. only the first 4 threads before the shoulder are load bearing on a standard 60degree thread profile....

    pick which ever floats your boat or suits your application best.

  9. #9
    A spigot thread is mechanically far stronger as it can be used with a much smaller shoulder.
    Not important for some rifles, bit I know which I would use on a light weight barrel, and it wont be 1/2x20
    for a .243 or bigger.
    I have a perfectly functioning M14x1 thread on a barrel that is only 15mm diameter, can't do that reliably without a spigot.

    Neil.

  10. #10
    Quote Originally Posted by nowler View Post
    if ... the thread is cut to within a thou clearance, then there is no need for a spiggot.
    If you truly can cut threads to mate within 1/1000" clearance then of course you don't need a spigot.

    But I doubt that moderator manufacturers cut the female threads on their mods. to such tolerances.

    E.g. standard tolerance for an M14 fine thread pitch diameter is 12.994 to 12.854 mm i.e. nearly 6/1000"

    Are you saying that you measure the internal thread on the mod. then precisely thread the barrel to achieve a 1/1000" clearance ?

    If so, I'm impressed. And would be interested to know how you measure the internal thread ?

    But you would also have no guarantee that any other mod. would fit.

    Machining threads to very very tight tolerances is interesting, but not very practical in the real world.

    Whereas turning a simple spigot onto a barrel or boring one into a moderator to a tight tolerance, and measuring it, is dead easy.

    [QUOTE=nowler;756983 it won't do any harm and has some merit for people who can't machine to benchrest tolerances or like loose fitting threads, but it is certainly not necessary for people who can.[/QUOTE]

    Unless you are also making the moderator, then this discussion is moot. In the real world, people expect to be able to screw brand x moderator onto brand y rifle, with gunplumber z thread and will be pretty annoyed if it doesn't work. That's what tolerances are for.

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