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Need Advice on Concentricity Problem

 
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  #1  
Old 03-13-2014, 09:24 AM
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Need Advice on Concentricity Problem

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?
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  #2  
Old 03-13-2014, 06:57 PM
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Re: Need Advice on Concentricity Problem

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.
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Old 03-13-2014, 09:37 PM
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Re: Need Advice on Concentricity Problem

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..
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Old 03-13-2014, 10:14 PM
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Re: Need Advice on Concentricity Problem

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.
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  #5  
Old 03-13-2014, 10:38 PM
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Re: Need Advice on Concentricity Problem

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.
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Old 03-13-2014, 10:46 PM
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Join Date: Dec 2012
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Re: Need Advice on Concentricity Problem

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.
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  #7  
Old 03-13-2014, 11:27 PM
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Join Date: Jul 2012
Location: North Central Valley California
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Re: Need Advice on Concentricity Problem

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.
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