Pennsylvania Firearm Owners Association
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  1. #1
    Join Date
    Jan 2008
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    Bridgewater, New Jersey
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    Default Measuring Lands & OAL

    Hi Guys & Happy New Year to all.

    Just bought a Hornady OAL guage & comparator.
    Used it in my Colt Match HBAR II.
    Lands/OAL measurement was 2.010 while using the comparator.
    That gives me a conventional OAL (w/o comparator) of 2.39.
    Do these measurements seem accurate?
    How much of bullet jump to start out with?
    Should I just seat to published OAL & not use these tools?

    The bullet is a Hornandy 50 gr V max. Its length is 0.768 if that helps.
    There's no such thing as a good gun. There's no such thing as a bad gun. A gun in the hands of a bad man is a very dangerous thing. A gun in the hands of a good person is no danger to anyone except the bad guys."
    -- Charlton Heston, 15 Sep 1997

  2. #2
    Join Date
    Jun 2009
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    Apollo, Pennsylvania
    (Armstrong County)
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    Default Re: Measuring Lands & OAL

    I normally start with 0.010" off the OAL Gauge reading.
    You may get better accuracy a little "further away" or you may not. Something you gotta play with.
    Just watch out with your OAL and the round fitting and feeding in the mag or you will end up with a single shot.
    My 300WSM loves a 0.012" distance short of the lands, but the rounds wont fit in the internal mag well. So i went shorter.

  3. #3
    Join Date
    Jan 2008
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    Waynesboro, Pennsylvania
    (Franklin County)
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    Default Re: Measuring Lands & OAL

    Good tools for finely tuned loads. Give up the OAL measurement, except to determine if a round will magazine. OAL will vary slightly from bullet to bullet because the tip (meplat) of bullets are not consistent, so its not the best measurement to produce highly consistent reloads.

    Using the Hornady guage, seat a bullet, then use the comparator to measure (from the bullet ogive) to the base of the case. This gives you the distance to the lands. (I usually measure multiple times to get the most accurate result.) This figure becomes the basis for consistent reload measurements in that rifle. (Doesn't matter if you include the length of the comparator, because you have a consistent starting point.) This the bullet ogive to case base measurement, which becomes / remains the basis for adjusting seating dies and tweaking seating depth.

    Normally, start loading .010" - .020" off the lands (subtracted from the measurement obtained above, still measuring ogive to base). When you get a decent group by varying powder / charge, etc, begin tuning by adjusting seating depth. I usually test at +/- .002" or .003" increments, check results... adjusting as groups tighten or loosen.

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