Seating depth

Discussion in 'Reloading' started by Rickyrebar, May 8, 2010.

  1. Rickyrebar

    Rickyrebar Active Member

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    Dec 12, 2009
    Since I have started reloading, I have only reloaded 1 type of bullet (Nosler CT Ballistic Silver tip). I am going to try a different type (Nosler AccuBond).
    I have found that the 2 different bullets have different seating depths (COAL measured @ OGIVE, CT Ballistic tip = 3.275, AccuBond = 3.318).
    To determine my seating depth I am using a fire formed case with a slightly crimped neck with a sharpie colored bullet, chambering it 3 times recording the measurements then after determining the avg. subtracting .015.
    Is it common that 2 different types of bullets would have such variance in COAL? It seems odd to me.
     
  2. blackbrush

    blackbrush Well-Known Member

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    Apr 3, 2008
    Is this attributed to the locale of the ogive on the specific bullet?

    Several days ago, I used that small itty-bitty barrel bit that Darrell Holland sent to me with my new 708...he used a chamber reamer and cut for about 3/4" into the bore and included it with my rifle.

    I never had the guts to ask...

    But after a year or so of contemplating, I determined it is the most accurate method to set OAL I am aware of.

    Very consistent results!
     

  3. Gene

    Gene Well-Known Member

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    The Hornady Comparator will produce much more accurate results. Ogive is where the straight shank of the bullet stops and the taper to the tip begins. There are always differences between various brands and weights of bullets; even the same bullets within the same box or lot, can vary. Consistent seating to the same depth, after you know which OAL is best, is what you want. You need the comparator to do this.
     
  4. trueblue

    trueblue Well-Known Member

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    Ricky,
    To answer your question, it is common to have different COAL with different bullets, as their ogive measurement from base of bullet is different for each one.
     
  5. blackbrush

    blackbrush Well-Known Member

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    Gene,

    I better sit down with my Hornady Comparator and learn how to use it correctly. I felt months ago, when I took some measurements on specific bullets, I had it down.

    After going back to remeasure, I find I have quite a "spread" in values. Apparently I have no feel and poke some into the lands and others slightly touch...there has to be a way to consistently duplicate.

    Wally
     
  6. Gene

    Gene Well-Known Member

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    Wally, I have a confession to make. I have the Hornady comparator, bought it when Stony Point made them, and did not feel it was perfect. Then I bought the Davidson base and several nose pieces from Sinclair, and found them to be superior. But many readers are not familiar with The Davidson or Sinclair, so I recommended the Hornady. I take back that statement. Look at the Davidson Seating Depth Checker. It does provide spot on measurements. Of course, there are still differences in bullet ogives. I actually seat my bullets about .005" long initially, then work them down with the Redding micrometer seater until they are exactly where I want them.
     
  7. I kinda to this the redneck way. I take a sized, unprimed case and stand it up primer side down - I take a small round file and file right through the middle of the neck down to the shoulder. I then size it again. I take whatever bullet I'll be using and just get it started in the case with my fingers - then I unscrew the seating die a few turns and lower the arm to raise the bullet into the die. I screw the top of the die down until I feel tension, then a few more turns until I know it's started straight. I put it in the gun and close the bolt firmly, then carefully eject the shell and measure and record the overall length. I do this three or four times (you can pull the bullet back out of the neck with firm finger pressure) until I'm certain that the measurement is correct. I start loading by subtraction .02 from that overall measurement. It has worked well for years.
     
  8. Mikecr

    Mikecr Well-Known Member

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    The ogive(o-jive) of a bullet nose is not a specific place. Ogive only defines the nose 'shape' in cals of radius. It defines the curve of the full nose length.
    The point where a bullet nose begins is just that, and really has nothing to do with land contact point(datum) on a nose.
    So two bullets measuring same base to bearing(nose begin), could have completely different ogives(ogive radius), and end up different distance to lands even though measuring the same with your tool. That is, if your tool doesn't measure atleast near the contact datum of the nose.
    I use a Sinclair 'nut' for every cartridge/bullet. Seems to work perfect, and marks very near contact marks.

    When you change bullets, you have to redefine jam, for that bullet, in that barrel. Then adjust seating from there as you had before(ie, -5thou).