Seating Depth Procedure

Discussion in 'Reloading' started by robdaniels, Mar 4, 2014.

  1. robdaniels

    robdaniels Well-Known Member

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    I am working on finding the rifling for a Sierra Game King 150 in a 270 WSM. I am using a black sharpie to color the bullet black and measuring with a hornady bullet comparator. I seat the bullet long just so the bolt closes. Take it out and I see the rifling marks all around the bullet. Ok good so far. I keep seating a few thousandths at a time until the marks begin to disappear. Then there is only one mark left and this last mark will show for a long time after the others have disappeared. I mean 20 to 25 thousandths. Once this mark is very faint I call it done and that measurement is what I write down as the beginning of the rifling's. I then seat the bullet 2 thousandths off that measure.

    Is it normal to see that last rifling mark so long after the others have disappeared?

    Thanks
     
  2. brentc

    brentc Well-Known Member

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    I believe what you are seeing is the drag mark from your ejector pushing on one side of the case head forcing the bullet to drag as its being pulled from the chamber. Your land measurement should start from where you last saw the marks around the entire circumference of the bullet.
     
  3. robdaniels

    robdaniels Well-Known Member

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    Thanks, I was thinking that last mark may be a drag mark.
    I'll start over again.
     
  4. supercrossbmx69

    supercrossbmx69 Well-Known Member

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    I tried the sharpie trick and it didn't work well for me. Try this, back your seating die way out and seat a bullet in a case. Stick it in your chamber and your bolt more then likely won't close. So twist your die more and more until your bolt closes. Take the case out and take some 0000 steel wool and polish the bullet. Stick it back in the chamber, extract it, and you should see all the marks of your rifling. Keep doing this slowly, (1-5 thou at a time) polishing the bullet every time you pull it out of the chamber until the rifling marks dissapear. You now have your OAL.

    In my opinion this is a way more accurate way to find your OAL then the OAL gauges that you screw into the modified cases because they do not take into account the amount of pressure put on the case by the bolt face when it is closed.

    Hope this helps.
     
  5. g0rd0

    g0rd0 Well-Known Member

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    what I do for all different bullets I use
    1. neck size and clean
    2. using 3 in1 oil lube the inside of the neck and the bullet at the base
    3. place bullet in the neck and push it in just enough to hold it
    4. chamber the dummy (the bullet will be seated at the rifleing).
    5.I now have the oal for that bullet, I measure then insert into my seating die with the seat adjuster all the way up. Screw it down to the bullet then I adjust it to seat it down another .005"
    I place this in the package with the rest of the bullets for ease of die set up.
     
  6. robdaniels

    robdaniels Well-Known Member

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    1. Wouldn't polishing the bullet each time with #0000 steel wool remove a thousandth or two, there by changing the measurement?

    2. Jamming the bullet into the lands then backing off .005 could still have the bullet sticking into the lands I would think. I am working with a 150 gr SGK and the length of the ogive is long. If I stick the bullet into the lands then I can still seat it another 20 thousandths and still see rifling marks.

    I did it again last night and worked the depth very carefully until all the marks just began to disappear. Called that measurement good and seated .002 deeper.
     
  7. Gene

    Gene Well-Known Member

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    No, 0000 steel wool will not remove enough copper to matter. Use a comparator of some sort to approximate the distance to lands. Always do this without primer or powder in the case. If you can remove the firing pin, you will get a better feel when bullet hits the leade. With some factory rifles, seeing the land marks is difficult. Many will not show consistent contact marks by each land. Always start seater about .015" above the touch marks. Do not lubricate inside case neck. Work down .005" at a time until marks disappear, then pull bullet slightly up and re-set seater higher by several thous until you can see contact. I use a 6x jewelers loupe to do this.