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Installing barrels

n/an/a Member Posts: 168,427
edited January 2014 in Ask the Experts
What insures threaded barrels are turned and tight with the sights where they belong?

Maybe I am missing something.

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    mrbrucemrbruce Member Posts: 3,374
    edited November -1
    The amount taken off the shoulder determines that......
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    llamallama Member Posts: 2,637 ✭✭
    edited November -1
    quote:Originally posted by mrbruce
    The amount taken off the shoulder determines that......


    Or it depends on what rifle you are talking about...

    On the FN-FAL and L1A1 different size locking shoulders are used
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    MIKE WISKEYMIKE WISKEY Member, Moderator Posts: 9,987 ******
    edited November -1
    a lot depends on which rifle you are talking about. most bolt actions are barreled and then the sights are installed. I just installed a 03a3 barrel and that required 4 trips to the lathe to get the front sight t.d.c.
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    n/an/a Member Posts: 168,427
    edited November -1
    The amount taken off the shoulder determines that.....

    What is a locking shoulder guys?
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    Tailgunner1954Tailgunner1954 Member Posts: 7,734 ✭✭
    edited November -1
    quote:Originally posted by Sage1
    The amount taken off the shoulder determines that.....

    What is a locking shoulder guys?


    What the barrel tightens up against. Most barrels tighten up against the front of the receiver, some (like Mausers, for example) tighten up against the inner ring.
    If you know the number of degrees the sight is off when the barrel is tight, and the thread pitch of the barrel, you can calculate the amount of material that needs to be removed from the barrels seating surface.
    IE a 10 TPI thread moves 0.100 per 360^ rotation (1"/ pitch = distance / turn). .1"/360^= 0.0028" (0.0027777... if you want to be fussy) per degree. To move the sights 10^ you would need to remove either .028" or .072" depending on which direction the sight needs to move. The chamber may need to be re-cut, depending on what the original headspace was at.
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    beantownshootahbeantownshootah Member Posts: 12,776 ✭✭✭
    edited November -1
    quote:Originally posted by Sage1
    What [e]nsures threaded barrels are turned and tight with the sights where they belong?


    A competent gunsmith. [;)]

    OK, answer has been given already. It depends on the exact model of gun you're talking about.

    With some guns, the barrel is installed FIRST, THEN the location for the sight is determined, the sight dovetail cut and the sight installed. That's the conceptually easiest way to do it.

    With others, you need to remove material from where the barrel mates with the gun (ie the "shoulder") to alter how far the barrel screws into place, and thereby control the absolute orientation of the barrel (and sight).

    Needless to say, you do need to know what you're doing here and have the proper tools to remove precise amounts of metal.

    Again, depending on the gun and what was done, once the barrel is installed you may need to re-cut the chamber to re-headspace the gun. For a revolver, you might need to recut the forcing cone.

    With some gun designs (eg FAL) the shoulder that controls the barrel seating depth itself can be removed and changed, potentially making this operation a little easier.
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    n/an/a Member Posts: 168,427
    edited November -1
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    MobuckMobuck Member Posts: 13,858 ✭✭✭✭
    edited November -1
    You figure the degrees required to index the sight to TDC. Then calculate the degrees vs thread pitch into linear measurement to determine the amount to take off the barrel shoulder. Keep in mind there will be a "crush factor" involved in the final torqueing of the barrel.
    The last barrel I installed that had sights was an 03A3. The new replacement barrel was timed perfectly and all I had to do was tighten it till the front sight was 90* to the bottom of the action.
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    tsr1965tsr1965 Member Posts: 8,682 ✭✭
    edited November -1
    Not all rifles are created equal. Savage has gotten around this, by tightening the barrel, until it headspaces properly, then using a lock ring, on the barrel, in front of the receiver to lock the barrel in place. Much like a castle nut on a collapsible stocked AR-15.

    As for the rest, it goes pretty much like Tailgunner says, and there ae several ways you can index the sights, and make headspace. It all depends on the gunsmith, and how much experience/knowledge they have. For those who build tack driving rifles everyday, it is like second nature to them, kinda like putting a nut on a bolt.

    Best
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    nononsensenononsense Member Posts: 10,928 ✭✭✭✭
    edited November -1
    quote:The new replacement barrel was timed perfectly and all I had to do was tighten it till the front sight was 90* to the bottom of the action.
    ?

    It's a good exercise for learning the relationship but you'll learn to do it by eye in business. You can guesstimate the number of degrees and hopefully be just a tad under on you estimate then make a tiny correction to come to TDC. But I'll have 5 of these done before you can accurately measure the correct number of degrees and then do the math.

    Always be sure to make both shoulders (action and barrel tenon) parallel and perpendicular. Any irregularities on either face will result in faulty measurements and inaccuracy of the finished product.

    Be sure that all surfaces are clean before test assembly or final assembly as tiny chips and dirt will affect fit and timing. There is nothing more disheartening than doing the final assembly only to find that there must have been a small irregularity (dirt, chip) involved in the last fitting and the timing is too far past TDC.

    The last check is for headspace and the correction for it. Be sure to NOT go too deep as this will result in a setback and re-timing...

    Best.
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