Seating Depth Variation

Discussion in 'Reloading' started by bill123, Apr 20, 2014.

  1. bill123

    bill123 Well-Known Member

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    I’m using 167 grain Lapua Scenars in Lapa brass, a Redding micrometer seater and Forster Co-Ax press. I’m measuring base to ogive w/a Hornady bullet comparater.

    Typically out of 40 rounds, I get around 50% right on my 2.269” CBTO goal measurement. Maybe 25% are over by .002” and 25% are under, some by as much as .006”.

    I’ve tried an RCBS press and a Harrel press, RCBS and Forster micrometer dies. I seat the bullets slowly and evenly.

    Typicall with the bullets that are under length, I “pull” them with an Impact Bullet Puller and reseat. When I reseat, there isn’t always a 1:1 ratio between the micrometer setting and the increase in depth of the bullet. In other words, I can screw down the micrometer and the bullet does not always go down a corresponding amount.

    My suspicion is that the variance is caused by slight anomalies on the bullets. My questions are:

    Am I right?
    If so, Is the initial seating the right seating and I should leave it alone?
    Am I doing something wrong in seating?
    Will reseating after pulling a bullet reduce accuracy? I don’t seem to lose any concentricity.
     
  2. Barrelnut

    Barrelnut Well-Known Member

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    I usually attribute this to different neck tensions with the brass. I always keep all brass in the same lot together and keep the fired round count the same on them. If you have brass from different lots, annealing can help too.
     
  3. Broz

    Broz Well-Known Member

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    Is your die set up to cam over on the shell holder? If not try this.

    Put a piece of brass in the shell holder and lower the handle to extend the ram up to full stroke. Then screw the die in to contact the shell holder. If the die stops before contact on the shell holder , you need to back it off 1/4 turn and set it there. If the dies will screw in all the way, without contacting the case, and touch the shell holder then back the ram down and screw the die a little deeper to get a slight cam-over effect at the end of the handle stroke. Lock the die lock ring while the ram is camed over and tight.

    This will take away the variation of ram stroke speed, and eliminate other slack in the system or operation that could be varying your seating depth.

    Jeff
     
  4. FearNoWind

    FearNoWind Well-Known Member

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    I believe the Lapua Scenars are tanget ogive bullets. If you seating die stem is machined for secant ogives it can make a difference in seating consistency. I'd check that possibility first.
    Of course, it's important to make sure you seater dies (including the seating stem) are clean and free of any lubricants. A film of lubricant can produce inconsistencies in seating depths.
    Any other ideas I might have had have already been mentioned.
     
  5. bill123

    bill123 Well-Known Member

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    Jeff, the redding directions say not to allow the shell holder to contact the die body. They say that the die could becomes waged to the point that the sliding sleeve no longer moves freely. Is this a real concern?
     
  6. bill123

    bill123 Well-Known Member

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    Thanks for the reply. I've had the same problem with 175 SMK's as well. I'll try taking the die apart and cleaning it.
     
  7. Broz

    Broz Well-Known Member

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    Well for a gorilla that greatly over does the "Light cam over" maybe after 100,000 rounds.:)

    I take it you have a Redding competition seating die with the micrometer top and retracting sleeve? If so that's what all my dies are and how they are set. By the way, a Redding tech named Robin ( great guy!!) taught me this method years and years ago. But if you feel it may damage your equipment then you should do as you see fit.

    Jeff
     
  8. bill123

    bill123 Well-Known Member

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    That's the die. Sounds reasonable. I'll try it. How much CBTO variation do you get from round to round?
     
  9. jrock

    jrock Well-Known Member

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    Had a similar problem and annealing the brass fixed it.
     
  10. bill123

    bill123 Well-Known Member

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    Thanks. I actually just solved my problem. Similar solution. Previously, I was sizing and letting the brass sit in a bin for a while, maybe 2 months. Seating was really rough. I just tried sizing some brass and seating immediately. Out of 20 rounds, I only had 2 that were .001" off of my target depth.
     
  11. Gene

    Gene Well-Known Member

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    Be very careful of using the "cam over" sizing method. It can push the shoulder back excessively, resulting in too much headspace and a FTF.

    I use Redding micrometer dies for seating. First I know where my bullet will kiss the lands. Then I decide where I want them seated: how many thous in or out, write it down. I set the micrometer about .010" higher than desired, measured with a Hornady or Davidson comparator (I prefer the latter). My loading block is numbered on the side from 1 to 10, meaning thous over. I seat bullets 10 at a time, and place each in the block according to how many thous I must reduce the OAL. From that point on its easy to hit the desired length right on.
     
  12. bill123

    bill123 Well-Known Member

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    Gene. Thanks for the heads up.