Neck runout dilemma

Nvhunter92

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so I'm resizing once fired brass in an rcbs press with a gold metal match bushing die. I was getting bad runouts after neck sizing so I tried floating the shell holder and got some odd results, see below;

Case 1: ro before .0015 after .0075
Case 2: ro before .001 after .00125
Case 3: ro before .0005 after .002
Case 4: ro before .0018 after .00025
Case 5: ro before .002 after .0005
Case 6: ro before .00025 after .003
Case 7: ro before 0 after .0022
Case 8: ro before .001 after .001
Case 9: ro before .0005 after .002


Why are my concentric cases getting worse and my non concentric cases getting better?
 

Mikecr

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Are you measuring runout or eccentricity?
How much are you down sizing?
What are the neck thicknesses & variance?
Are you expanding necks?
 

J E Custom

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Texas
Don't know if this is your problem, But I have found that if I turn the necks just enough to clean them up before I fire the cases the first time it trues up the neck thickness and prevents the neck from being pushed off center by the difference in the wall thickness of the un turned neck.

When I buy new cases, i always turn them just enough to clean them up, especially on my wildcats that will be sized up or down. from this point on the chamber keeps the case true to center and case runout is held to a very minimum and only poor loading will throw them off. with some dies it works better to rotate the caes halfway through the bullet seating process.

Works for me

J E CUSTOM
 

Nvhunter92

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Elko, NV
Are you measuring runout or eccentricity?
How much are you down sizing?
What are the neck thicknesses & variance?
Are you expanding necks?

I'm measuring runout and am not using an expander. It's just weird that if I put a case with low runout through my neck sizer it comes out with high runout, but when I put a case with high runout through the sizer it comes out with very little runout...
 

Mikecr

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So this is a 'FL sizer bushing(body-bushing) die' ?
What runout gauge are you using?
Have you measured thickness at necks?
 

Nvhunter92

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Location
Elko, NV
So this is a 'FL sizer bushing(body-bushing) die' ?
What runout gauge are you using?
Have you measured thickness at necks?

It's a bushing neck sizing die, I'm using the rcbs concentricity tool. The necks are turned to a consistent .014". But with the bushing it should squeeze all the inconsistencies to the inside and not register neck thickness variance on the concentricity tool
 

bigedp51

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Dec 10, 2010
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At the Whidden custom die website they tell you that they get the most concentric cases with non-bushing full length dies. And Whidden does not make neck sizing dies so this should tell you something.

1. With a neck sizing die it does not fully support the case body in alignment with the case neck during sizing.
2. If reducing the neck diameter over .004 with a bushing die it can induce neck runout.
3. If the case body is thinner on one side the case can bulge on the thin side making the case egg shaped. Meaning the runout can be coming from a egg shaped case when spinning the case on its body.

And Forster full length benchrest dies with their high mounted floating expander produce very concentric cases. (subliminal suggestion)
 

DUSTY NOGGIN

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salt lake city
And Forster full length benchrest dies with their high mounted floating expander produce very concentric cases. (subliminal suggestion)

^^^^ this helps before first firing right after turning off neck for the first time (( thumbs up ))

i do this with my rcbs FL dies too , lift it high enough that you do not feel a gap between then i usually go about 2 full rotations higher on the seater plug and not tighten the jam nut , until it is squeezing the neck in the body and the inside of the neck on the expander ( at the same time ). if that case comes out concentric , i leave the jam nut on the expander rod tight ... for when you are trying to correct out of whack once fired brass ...
 

DUSTY NOGGIN

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too small of bushing ??? all at once ?? or sizing too close to the shoulder

anneal em before next sizing ,

what is the fire measurement compared to the sized measurement

if a guy was to mark the high side of his worst cases in the batch and rotate them in the neck sizer and see if you get any correction --
 
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