Bullet seating discrepancies - Don't know why

Discussion in 'The Ammo & Reloading Forum' started by .308 shooter, Aug 25, 2008.

  1. .308 shooter

    .308 shooter New Member

    Joined:
    May 3, 2008
    Messages:
    100
    Okay, I've chosen the cases that are the correct length. I loaded approximately 30 cases starting with the minimum charge for the bullet powder combination I'm using.

    I seated the bullet to 2.81" per the manual with this being the maximum COL. I chambered it in my rifle (Savage 10FP - bolt action) and the bolt closed fine (and the cartridge was not primed or charged). I locked down the die to ensure the seating wouldn't change and proceeded to fully load the cartridges and measured every one after seating bullet. My measurements ranged from 2.808 to 2.815.

    If the die was locked down to the correct size, the why difference in sizes?
    I double checked all the loads and got the same results. I've got 6 that are either 2.814 or 2.815. What would cause this?

    I realize this may be minimal, but I'm wondering why this would happen. Should I pull the bullets, recharge and reseat?
  2. LDBennett

    LDBennett Well-Known Member

    Joined:
    Dec 20, 2003
    Messages:
    6,771
    Location:
    Hesperia, CA
    The overall measurement is not a good measurement to use as a comparison between loaded cartridges. I know its all confusing but rather than just reloading and shooting your reloads, you are asking questions some reloaders never ask until they have been doing it for years.

    The correct measurement method is to use a bullet nut (comparator):

    http://www.midwayusa.com/eproductpage.exe/showproduct?saleitemid=365474&t=11082005

    or

    http://www.midwayusa.com/eproductpage.exe/showproduct?saleitemid=746974&t=11082005

    This device allows a comparative measurement between cartridges but uses the bullet Ogive rather than the end of the bullet. The seating die does not seat the bullet by pushing on the bullet end but by pushing on the bullet Ogive (part of the nose of the bullet). So every bullet is seated the same from the bullet Ogive to the case head.

    You set up the OAL on a test cartridge per the book spec (or other more advanced methods that you don't need to know about just yet) using the OAL. Then you slip the bullet nose into the nut in the hole for the caliber of interest (30 cal for 308) and measure from the other side of the nut to the cartridge base with calipers. You record that number and all cartridges should match that number when measured this way. Any ammo made in the future should be gaged the same way and made to match the same number for this bullet.

    OK?

    The way bullets are formed, any excess material ends up protruding into the end of the bullet nose. Every bullet is the same except they might end up with small differences of the excess materials in the end of the nose. In a box of bullets you'll find big variations in the length of the bullet but very small variations when using the comparator nut. If the bullets were made perfect you could not afford to buy them! This way gives the most accurate bullet for the least cost. Accuracy is not affected by this manufacutring process normally.

    LDBennett
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