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Thread: Barrel Thread

  1. #1

    Barrel Thread

    Hi Gents, I have a spare Blaser barrel in .308 with fixed iron sights.
    I wanted to move the front sight back just enough to get the barrel threaded.
    The gunsmith suggested a 15x1 spigot but that would put at least 3" of muzzle in front of the sight and make the distance between front and rear sight about 14" making the whole setup look out of proportion.
    So I suggested having a 1/2"x 20unf thread which would only leave the diameter of the barrel forward of the muzzle, making it look a little better.
    However, when I mentioned the 1/2" thread you would have thought I'd just told him I eat babies !!
    His hands went up and his eyes nearly popped out of his head with shock.
    He asked if I was serious and when I said yes, he wanted me out of his shop straight away !!
    (a bit of poetic license there really)
    What he really said was that he did not recommend a 1/2" thread on a .308 and suggested I think again.
    I have had a 1/2" thread on a Remington .308 for a few years and had no problems, so I would like to throw this question open to the learned members of this site and any gunsmiths that may be lurking, why is a 1/2" thread not recommended for a .308 when it is probably the most common thread used across the board.

  2. #2
    Eddie, we discussed this some time ago.

    Gwt the 15x1 spigot and mount the foresight on the thread cover.

    Photos tomorrow. Steve Kershaw will do the work.
    Brian.

    Just because you are paranoid, doesn't mean they aren't out to get you......

  3. #3
    my Howa has a factory 1/2" thread and its .308 on a sporter profile barrel, is the problem due to the reduction in barrel diameter if you use the same thread with a varmint or heavy barrel? ie cosmetic?
    "Politicians must be allowed to panic. They need activity. It is their substitute for achievement"
    "'The matter is under consideration' means we have lost the file. 'The matter is under active consideration' means we are trying to find the file."

  4. #4
    Moving the sight back is not that easy, it is (if like mine) held by a spot welded stud, not a threaded hole for a screw.
    If you are keeping the sight on the rifle all the time you are limited to a muzzle can, in which case I'd have to side with the smith you have spoken to already.

    I'm in the same boat at the moment, I have a new to me rifle, have had it for a while now, but not pulled the trigger and can't until it wears a mod.
    But like yours it has iron sights that I want to keep, and being a thin profile barrel and a .30 cal a x 20 thread is out of the question.
    I think I'm going to go with an M14 with spigot and just move the sight back, with the right mod you only need to move it back 30mm

    Neil.

  5. #5
    1/2" unf 20 isn't ideal but sometimes that's all you have to play with, however, I'd go with 1/2" unef 28 (almost 1mm pitch) as it's a finer thread allowing more surface either side, not much granted. I wouldn't go with a spigot, waste of a barrel, if the thread isn't cut true then it shouldn't be cut in the first place. My Blaser from many years back had a thread and screw to secure it but I guess that might of changed. I would suggest that a re proof might be necessary if the barrel is tapped and threaded, not too much of a difficult job to do.

  6. #6
    Quote Originally Posted by Hornet 6 View Post
    Moving the sight back is not that easy, it is (if like mine) held by a spot welded stud, not a threaded hole for a screw.
    If you are keeping the sight on the rifle all the time you are limited to a muzzle can, in which case I'd have to side with the smith you have spoken to already.

    I'm in the same boat at the moment, I have a new to me rifle, have had it for a while now, but not pulled the trigger and can't until it wears a mod.
    But like yours it has iron sights that I want to keep, and being a thin profile barrel and a .30 cal a x 20 thread is out of the question.
    I think I'm going to go with an M14 with spigot and just move the sight back, with the right mod you only need to move it back 30mm

    Neil.
    Depends how thin the barrel is as to whether a 14x1 spigot will go on it.

  7. #7
    I too recently encountered a gunsmith who would not thread 1/2 inch 20 on 308 Winchester. Apparently it is too narrow a diameter leaving a very thin barrel wall. Apparently over time this section of the barrel distorts as a result, which can be seen with a bore scope.

    i left the choice of thread to his discretion, and he went for one of the metric ones. In my mind this is no bad thing. I won't confuse the mod with my 243 one and don't ever intend to sell it.

  8. #8
    If you do some basic maths you will see why 1/2" isn't a good idea for a .308.
    .308 = 7.62mm
    1/2" = 12.7mm
    12.7 - 7.62 = 5.08
    5.08 divided by 2 = 2.54mm which is the thickness of barrel left with this size thread!
    Not much meat there when you consider the forces going on when a .308 goes bang!
    I also can't see the point of a spigot? Just another waste of good barrel metal.
    A 5/8" without a spigot or metric size of +15mm would be the better option.
    MS

  9. #9
    It's the wall thickness of the barrel that's the issue, this coupled with the depth of thread and the relief cut for the shoulder which needs to go deeper than the bottom of the thread. The actual thread itself is ok but I prefer a finer pitch.

    I thread two the other day, wall thickness was fine, it was the shoulder that was the issue, less than 1mm either side before thread, hence I had to go 1/2" unef 28, the other had 1.6mm after threading a 14x1.
    Last edited by Jager SA; 13-12-2013 at 09:03.

  10. #10
    I wonder if the aversion to English threads is more to do with having to swap the lathe over to English from metric which I guess it was already set up for.

    Myself I don't like metric threads their simply too sloppy when cut to match the gauges. Of course it also seems not many "barrel threaders" use gauges they just use the mod and rely upon others threads.

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