finding size to turn necks to

Discussion in 'Reloading' started by Ua26fitter, Oct 17, 2018.

  1. Ua26fitter

    Ua26fitter Well-Known Member

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    Would it be fine to measure my reamer to find the size to turn the necks to? I realize that you want about .002 smaller than the chamber neck for the brass.
    my reamer measures .338 so if I turned my brass with a bullet seated to be no larger than .336 I should be set. I haven't been able to find anything where someone used the reamer to find the size of the chamber neck.

    I've never neck turned before so I figured I might give it shot.

    Kris
     
  2. eklarsen

    eklarsen Well-Known Member

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    Yes, typically I would get the chamber dimensions from smith who did it but as you have the reamer you are good. 2 thousand clearance is perfect.
     
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  3. Ua26fitter

    Ua26fitter Well-Known Member

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    well I asked him last time I was in his shop and he pulled out the reamer and measured it in front of me.
    I figured it was good but being that I couldn't find anything with someone doing it that way I would throw it out to confirm.

    Thanks
     
  4. Wedgy

    Wedgy Well-Known Member

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    .002" is pretty tight and leaves little room for error, assuming this is a hunting gun ?? so I use a minimum of .003" or .004" .
    A BR gun with jammed bullets has a tighter set of tolerances than hunting guns.
     
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  5. Ua26fitter

    Ua26fitter Well-Known Member

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    Wedgy,
    thanks I'll go with a little more then.
     
  6. Wedgy

    Wedgy Well-Known Member

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    You can easily get some carbon build up on the chamber that won't allow the neck to open up and release the bullet.
     
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  7. Mikecr

    Mikecr Well-Known Member

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    One feeds the other.
    Going large in clearance CAUSES carbon to build up in chamber neck area. 2thou is PLENTY of clearance, and if you keep trim length within 5-10thou of chamber end you'll reduce carbon blowback even more, to mitigate carbon ring formation.
    It's also beneficial to size necks less, and 2thou clearance provides for this.
     
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  8. bigedp51

    bigedp51 Well-Known Member

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    For those of you with off the shelf factory rifles a .308 Winchester has a chamber neck .008 larger than the neck of a loaded round. Meaning approximately .004 clearance on each side of the case neck.

    And you have no control of how much the case neck expands in a SAAMI chamber, "BUT" you still have to reduce the neck diameter that .008 plus approximately .004 when sizing the case neck with standard dies.

    And the point I'm making is bushing dies work best with custom tight neck chambers and neck turned brass. And with a factory rifle most reloaders will not see any improvement in accuracy by neck turning their cases. And in another well known forum they are told to just buy Lapua brass and load and shoot without doing anything to the brass.

    There are benchrest rifles that never hunt dangerous game and hunting rifles that have more wiggle room in the chamber for reliable function in the field.

    And my old milsurp rifles have long fat chambers with plenty of case neck and case body clearance.

    The late Jim Hull of the Sierra ballistic test lab had a humorous saying about full length resizing.

    "The cartridge should fit the chamber like a rat turd in a violin case". Meaning give the cartridge a little wiggle room to let the bullet be self aligning in the throat. In fact the only part of the full length resized case that touches the chamber walls is the case shoulder when pushed forward by the ejector and firing pin.

    [​IMG]
     
  9. Wedgy

    Wedgy Well-Known Member

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    Mike, .002" total(.001" on each side) or .002" on each side(.004" total) ?
    I trim length to .005"-.010" as well.
     
  10. Ua26fitter

    Ua26fitter Well-Known Member

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    I believe it's. 002 each side
     
  11. DocDoc

    DocDoc Well-Known Member

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    I see reports of the .284 needing 0.003-0.004 clearance for best accuracy.
     
  12. Varmint Hunter

    Varmint Hunter Well-Known Member

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    I wouldn't bother with reamer specs because they assume that your chamber matches the specs provided and "may" not be accurate.
    I just carefully measure new brass that was fired in the chamber and work from there. Once fired brass is typically .001" smaller in neck diameter then the chamber. Subtract .002"-.003" from that measurement and you should be good to go in a hunting rifle and have a little room for error.
    Just my 2 cents
     
  13. Ua26fitter

    Ua26fitter Well-Known Member

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    we measured the actual reamer.
    Although I didn't realize I could measure fired brass also. I'll have something to compare it with.
    thanks.

    Kris
     
  14. eklarsen

    eklarsen Well-Known Member

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    Fired brass has expanded to fit the chamber but then retracts some, I would still use the reamer spec or measurement.