Need Advice on Concentricity Problem

Discussion in 'Reloading' started by BCMAG2, Mar 13, 2014.

  1. BCMAG2

    BCMAG2 Well-Known Member

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    I'm hoping someone can help me out with this concentricity issue. I'm a fairly experienced reloader. I use the Redding competition dies to load my 300 RUM and concentricity as measured on my digital Sinclair gauge is great--1.5 thou or less, and often all zeros.

    So I recently started reloading for my 280 Ackley with Nosler Custom brass, as its the only commercially produced brass for that cartridge. It comes out of the full length RCBS resizing die perfect almost every time--the necks measure a thousandth or less on the concentricity gauge. The occasional brass over that is run through the resizer a second time and always fixed. Then I trim to length and put a square VLD chamfer in the throat. I lube with graphite and load with a Redding competition seater die. With both the standard accubonds and the new long range accubonds, I very seldom get less than 2 thou of concentricity, and most come in right at my self-imposed limit of 3 thou. About a third run 4.5 to 6.5 thou, and I don't know why. Never had that problem with my 300 RUM using the cheaper Remington brass. I do also have the Hornady "neck bender" gauge that straightens the rounds out to 3 thou or less fairly easily, but I would rather not do that. It seems to me that the vast majority should be coming off the press at well under 3 thou concentricity, as they do with my 300 RUM. The only process that I can think of that I do not perform is turning the inside of the case necks. I have never found that necessary with the Remington brass. Perhaps the Nosler custom brass requires it for some reason?
    Any ideas why I might be having this problem?
     
  2. Mikecr

    Mikecr Well-Known Member

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    The difference seems unseated neck measure -vs- seated neck measure.
    This is not a problem in itself.
    What matters is runout off seated bullet bearing/noses.

    When you seat bullets in them low runout necks, you're sizing necks from the inside, pushing it's thickness variance outward, which you then read as increased runout. You wouldn't see that with turned necks.
    Check runout off seated bullets & decide if this is important enough (to you) to turn.
    Go back & check your 300RUM again also.
     

  3. clambdin

    clambdin Well-Known Member

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    I've noticed the same thing with nosler 280 AI brass, neck indicates less than .001 but bullet runout seated with a wilson inline seater often measures .003..the only thing I can think of is the 280 ackley brass has uneven neck thickness...most of my 300 WM loaded rounds run .001 or less bullet runout with nosler brass..
     
  4. BCMAG2

    BCMAG2 Well-Known Member

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    Mikecr,

    I didn't make myself clear enough. Unseated neck concentricity is great... .001" or less...and so is seated neck concentricity!--the measurement doesn't change, even when the seated bullet, measured at the ogive about .1" beyond the edge of the brass is as high as 6.5 thou out of alignment. That's the part that I just don't understand, along with the "why" that's happening on almost a third of my loads but only with this cartridge. Never had that problem with my 300 RUM, 270 Win, or 338 Win Mag.
     
  5. bill123

    bill123 Well-Known Member

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    Maybe the bullet is too long for the seater stem and the stem is pushing on the bullet tip instead of the ogive? Unscrew the seater, put a bullet in it and see where it's contacting.
     
  6. BCMAG2

    BCMAG2 Well-Known Member

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    That's a great theory where the LRABs are concerned, as they are very long and taper slowly to a sharp point. But I'm having the exact same issue with the old style accubonds too, and I don't believe they could be too long for a brand new RCBS die. But thanks for the idea.
     
  7. FearNoWind

    FearNoWind Well-Known Member

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    Two ideas to offer:
    1. When I changed from tangent to secant bullets , my Wilson in-line seater die skewed the loads more than I expected. I thought it impossible that the seating stem could be the source of the problem but when I replaced the tangent stem with the secant stem the problem went away.

    2. With my Redding seating dies I occasionally get a errant concentricity reading on perhaps 5% of my loads. To remedy that I first start the bullet into the neck, remove any pressure and turn the round about 180 +/- degrees, and finish seating it. No more concentricity issues outside of specs.
     
  8. BCMAG2

    BCMAG2 Well-Known Member

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    Thanks. I'll give your method of turning the brass 180 degrees after partial seating a try. Considering the high percentage of out of spec rounds I'm getting, I am dubious that will eliminate the problem, but it may help.
     
  9. LoneTraveler

    LoneTraveler Well-Known Member

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    The problem may be in the seating stem. Take the seating stem out of the die and put it in a lathe or drill where you can spin it. Check to see if the seating cone is out of line with the stem. Set a bullet in the stem and see if the bullet is contacting on the ogive of the bullet or on the point of the bullet. If the bullet is contacting on the point, Check with the die manufactor about a new stem. Good Luck in finding the problem.
     
  10. ramrod79

    ramrod79 Well-Known Member

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    Hey I just bought a 280AI ,and am using Nosler brass as well as ABLR bullets so let me know how you fair out as I will try out all your methods before I start my process so that I may not encounter the issue you are having.
     
  11. BCMAG2

    BCMAG2 Well-Known Member

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    Thanks for all the good ideas, guys. I have a Redding type S bushing FL resizing die heading my way. I'm going to give that a try over my current RCBS resizer before I start examining the bullet seating stem, but that will be my next step if necessary.

    In the meantime, I should clarify that even with the loads I'm getting, this light weight 280 AI still shoots great--half an inch MOA at 100 yards. So from that perspective, the bullet run out I'm getting could be deemed "good enough"...but we on this forum seldom view anything that's less than perfect "good enough"...here's a short video clip of my first data validation test with 168 gr LRABs at 2,950 fps MV. The face of the rock isn't much bigger than a softball at 672 yards...I used the BC for the 168 gr 7mm Berger VLD in my program, as I don't buy the BC that Nosler is claiming...

    [ame="https://www.youtube.com/watch?v=1st6E5l5WLo"]20131214165056 - YouTube[/ame]
     
  12. kraky

    kraky Well-Known Member

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    I can tell you from experience a seating stem pushing on the tip of a very pointed bullet WILL NOT seat bullets straight. I would strongly suggest you take a look at the fit...it would take seconds to do that.
    Then you can forget those 6" rocks and start picking on the 3" ones...they are the most foul and deserve eradication!
    Great job btw!
     
  13. BCMAG2

    BCMAG2 Well-Known Member

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    Thanks Kraky....I've also noticed that the further those rocks are from me, the more menacing and worthy of being shot at they seem! I had to take down one at extreme range with the 280 Ackley just this morning, to make the world a safer place for women and children, of course...

    https://www.youtube.com/watch?v=GslFYUz5YSw&feature=youtu.be
     
  14. AZShooter

    AZShooter Well-Known Member

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    Just read the entire thread. Nothing was mentioned about neck tension.

    What is the difference in neck OD of sized vs seated? Most RCBS FL sizers I have used will make a .003" difference. If it is .003" or more it may be too much tension when combined with the steep 40 degree shoulder. The seating pressure could cause the shoulder to yield causing your excessive runout.

    When you get your bushing die try using bushings that create .003" and .002" neck tension and see if less neck tension helps reduce runout values.