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Thread: OAL variation

  1. #1

    OAL variation

    What sort of variation do you guys get in your seating depth? I just measured some of my .270 loads and was suprised to see quite a difference in the length.
    I measured between 71.72mm to 71.84mm does this seem like a lot?
    bullet is a 130gn gameking, case is full length resized and trimmed to length. Dies are redding, press is a rockchucker.
    Any thoughts?

  2. #2
    Ezzy

    71.72 millimeters = 2.82362205 inches 71.84 millimetres = 2.82834646 inches

    2.824 inches to 2.828 inches is pretty good in my book. I try to get less than +-2 thou with respect to the nominal OAL I am going for.

    Well done. JCS

  3. #3
    I've known a very long time that OAL is difficult to maintain consistency within +/- .002". You cannot rely on the bullet OAL being consistent for this, nor indeed your cases - unless you have very carefully sized and trimmed them to exact length.
    Even so, the use of a comparator is the most reliable measuring device and provided the cases are indeed exact to matching OAL, careful & very consistent pressure on the ram lever just lightly touching the final point of the seating die, should yield the optimum consistency of OAL, more often than not, to within +/- .001"
    It's a slow process, but does work.......but the question is:
    Can you shoot to within the accuracy the rifle/crtridge combination will give?
    Do you really need this close tolerance level?
    Last edited by deeangeo; 23-08-2011 at 07:23.
    Blaser K95 Luxus Kipplaufbüchse .25-06Rem. Zeiss 8x56, 110gn Nosler Accubond = Game Over!

  4. #4
    Quote Originally Posted by deeangeo View Post
    I've known a very long time that OAL is difficult to maintain consistency within +/- .002". You cannot rely on the bullet OAL being consistent for this, nor indeed your cases - unless you have very carefully sized and trimmed them to exact length.
    Even so, the use of a comparator is the most reliable measuring device and provided the cases are indeed exact to matching OAL, careful & very consistent pressure on the ram lever just lightly touching the final point of the seating die, should yield the optimum consistency of OAL, more often than not, to within +/- .001"
    It's a slow process, but does work.......but the question is:
    Can you shoot to within the accuracy the rifle/crtridge combination will give?
    Do you really need this close tolerance level?
    Sorry, but why does case length (trimmed or not) affect OAL?
    Handle every stressful situation like a dog. If you can't eat it, hump it or learn from it then piss on it and walk away.

    "HOSPITALITY" - the art of making guests feel at home (when you wish they were).



  5. #5
    Quote Originally Posted by Eyefor View Post
    Sorry, but why does case length (trimmed or not) affect OAL?
    Trimming changes the length of the neck that grips the bullet and trimming adds burrs to the end of the neck which are then removed. All work on the neck has an impact on the consistency of the neck tension on the bullet. In my brass prep I attempt to get consistent necks (length & tension) and necks that are burr free. Regards JCS

  6. #6
    It depends on how you are measuring Ezzy.

    If you are measuring to the tip of the bullet, then .005" tolerance is acceptable as the actual length of the bullets will vary this much.

    If you are using a comparator and measuring to the ogive, then (In my opinion) .005" is rather excessive and you may need to look at
    your bullet seating methods and/or dies.

    However, Deeangeo is absolutely right. If the rifle/bullet combination accuracy is as you want it, then carry on as you are and enjoy it

  7. #7
    Quote Originally Posted by jcampbellsmith View Post
    Trimming changes the length of the neck that grips the bullet and trimming adds burrs to the end of the neck which are then removed. All work on the neck has an impact on the consistency of the neck tension on the bullet. In my brass prep I attempt to get consistent necks (length & tension) and necks that are burr free. Regards JCS
    I agree that neck tension is important but length of case will not affect to OAL to ogive - only the amount of bullet in the case, so therefore gives differing tensions?
    Last edited by Eyefor; 23-08-2011 at 08:30.
    Handle every stressful situation like a dog. If you can't eat it, hump it or learn from it then piss on it and walk away.

    "HOSPITALITY" - the art of making guests feel at home (when you wish they were).



  8. #8
    Measuring with a comparator from ogive will give a more consistent OAL as bullet lengths vary considerably, also it will help ensure you maintain the correct distance from the lands you want to achieve.
    Cheers,
    Last edited by deeangeo; 23-08-2011 at 17:40.
    Blaser K95 Luxus Kipplaufbüchse .25-06Rem. Zeiss 8x56, 110gn Nosler Accubond = Game Over!

  9. #9
    Stop measuring the OAL. You'll make yourself crazy if you think you can do a lot better than .004 variance.~Muir

  10. #10
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    If you want to get a more consistent measurement use a comparator and measure all your bullets base to ogive length
    and batch them, you will find even match bullets vary as much .005", I have done this several times and it is a total waste time especially with a hunting rifle, you are better off tweaking your powder charge a couple of tenths of a grain.
    Robert.

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