Seating depth/COAL?

Discussion in 'Reloading' started by RMulhern, Aug 30, 2010.

  1. RMulhern

    RMulhern Well-Known Member

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    Any of you guys ever had much luck obtaining top accuracy when you were using a BT bullet whereby it had to be seated deeper than normal so the bolt would close?? By normal depth...I mean whereby the upper portion of the BT was even with the bottom of the neck.:rolleyes::rolleyes:
     
  2. J E Custom

    J E Custom Well-Known Member

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    Seating depth makes the most difference to the lands . if you have to seat a bullet deeper
    to get it in the mag box it only takes up powder space.

    If you have little or no head space it will shoot good even well off the lands.

    On some cartriges (Like the 300 Win Mag) that have a short neck it is common to deep
    seat the bullets.

    J E CUSTOM
     

  3. RMulhern

    RMulhern Well-Known Member

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    JEC

    Thanks! What's been 'bugging me' is that I've tried shooting some Berger 130 grainers in my 6.5x47Lapua and I have to seat these rather deeply to be able to close the bolt. Quite obvious it's not a 'throated chamber'; just a standard cut. At 1000 yds. and using 38 grs. Varget the accuracy is MUCH LESS than what I can obtain with Sierra 123 gr. HPBT. It's been my experience over many years that if a bullet had to be seated with the base of the bullet back down into the main portion of the powder area that accuracy would suffer! Seems like I'm experiencing that with the endeavor to shoot the Bergers!:cool::rolleyes:
     
  4. boomtube

    boomtube Well-Known Member

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    "If you have little or no head space it will shoot good even well off the lands."

    I'm confused about that observation; headspace is where the cartridge fits. If there's "no head space" we can't chamber the round. ??


    I don't think the accuracy if a cartridge is firmly related to where the base of the loaded bullet sits. Seems it's the jump to the lands, concentricity and tuning the charge to the barrel that matters.
     
    Last edited: Aug 31, 2010
  5. J E Custom

    J E Custom Well-Known Member

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    Think of it this way, if there is no head space the bolt closes with a little resistance but it is
    lined up perfectly/Concentric with the bore if it has been fire formed and turned.

    This is the reason I turn the necks before firing. the chamber is very concentric and holds the
    bullet centered because of the shoulder wants to center and the bolt holds the cartrige square
    (If it is trued).

    If you chamber a round that is sized to fit any chamber in a chamber with .002 + head space
    the round will lay in the bottom of the chamber and the bullet will not line up with the bore
    properly. (Granted it's only a few thousandths) but it does make a difference.

    That is the reason most shooters interested in accuracy neck size only after fire forming.
    fire formed cases have No headspace and hold the bullet centered even though the neck
    diameter is smaller than the chamber to allow the bullet to be released .

    If you are not into reloading and will only use factory ammo I would never chamber this
    tight because some factory ammo would not fit. also for a new to reloading shooter I
    would recomend .001 to .002 headspace to start with and as he gets better he could
    neck size only and end up with the best of both worlds.

    If all things are right/true in a rifle ,zero head space will produce great accuracy with
    lots of freebore because everything is lined up and Centered also brass life is increased
    greatly because it dies not have to expand as much stretching the brass upon the
    first fireing.

    I hope this answered your questions.

    J E CUSTOM
     
    Last edited: Sep 1, 2010