OAL consistency

Discussion in 'Reloading' started by rclouse79, Sep 26, 2010.

  1. rclouse79

    rclouse79 Member

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    I was making some 270 cartriges with 130 grain nosler accubonds. I had the bullet seating die set so that most of the cartriges were 3.340 +- .001. Every few bullets would be up to +- .008. Is this most likely due to a difference in the tips of the bullet or am I doing something wrong.

    I end up setting the bullets that were over aside and reseated them a bit deeper.
     
  2. jimbires

    jimbires Well-Known Member

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    this is a difference in the bullet tip . a better way to measure is with a OAL tool that measures from the ogive of the bullet . Hornady makes one that works well , it clamps on your caliper . the ones you set aside and shortened up will be to short when measured with a ogive tool . I'd either pull the bullet a little and reseat them , or use them for fouler shots at the range . Jim
     

  3. woods

    woods Well-Known Member

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    There are a lot of factors that will cause inconsistant seating depth

    1. Inconsistant bullet bearing surface and meplat to ogive dimensions (the Accubonds have been the worst offenders for me)
    2. Differences in ID of the neck (common with unturned necks sized with bushing dies)
    3. Differences in the finish of the ID of the neck which will cause different compression on your press linkages
    4. More work hardening of the neck which will cause harder seating
    5. Poor contact of the seating stem on the ogive of the bullet

    IOW, more seating pressure will cause a shallower seating depth

    In case you're skeptical of the inconsistancies in Accubonds, an illustration here with a couple of 200 gr Accubonds from the same box

    [​IMG]
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    [​IMG]
    [​IMG]
     
  4. Derek M.

    Derek M. Well-Known Member

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    take a hard look at what Woods posted. He's correct. Don't worry about the COAL from tip of bullet to case head other than whether or not it will fit in your magazine. The critical OAL to be concerned with is at the ogive. This is the part of the bullet that begins making contact with the lands.
     
  5. LRHWAL

    LRHWAL Well-Known Member

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    This is why I prefer a bit of jump to on the lands - it's more forgiving of variations in COL.

    Woods summed it up.
     
  6. boomtube

    boomtube Well-Known Member

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    OAL works in two ways; 1) Does it fit the magazine and chamber properly? 2) Does it help acurracy?

    For accuracy it only matters how far the bullet travels before hitting the rifling, not the OAL per se. No rifle cares where a bullet tip hangs in space, so work off the ogive.
     
  7. Varmint Hunter

    Varmint Hunter Well-Known Member

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    I'm currently working with the 225gr Accubond in a 338 RUM. When seating the bullets and measuring from the ojive to the cartridge case base I noticed a frequent .010" variation. I double checked to ensure that primers were seated properly and that there was no powder compression (2 things I've noted can cause this problem) but everything looked good. I called Nosler who was pretty sure that the bullet tip was hitting the seater stem. That wasn't too likely because the 300 SMK and 185 TTSX bullets all seated within .001" consistently and they are both more pointed than the Accubond.

    Eventually, I bought a set of Redding competition dies and guess what - the Accubonds continued to seat .010" differently while the other bullets did not. Personally, I think I've got bullets from 2 different lots or produced by 2 different machines in one box of Accubonds. I can't think of any other explanation.
     
  8. Boss Hoss

    Boss Hoss Well-Known Member

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    OAL tells you nothing except if it will fit into a magazine. Need to know the bearing surface and go from there---OAL will tell you nothing when you get into fine tuning your loads