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Reloading Berger Bullets


Case Cocentricity

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Unread 12-01-2008, 03:36 PM
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Re: Case Cocentricity

"The expander ball does .004" of bending if used in the same step as when the brass is sized,..."

Clark, you bring this up for the second time. I have found no such predictable results in my use of various expanders. Many of my necks are bent less, a few are much less, while a few are greater. Mostly it seems dependant on the indivitual case. So, I wonder how you arrive at such a specific tilt number.

In your experience, does the length of the case necks matter? Or do the various designs of expanders, inculding those very different styles made by RCBS, Hornady, Lee, Lyman's "M" or one of the carbide expander balls, make any difference in your .004" tilt figure?

Last edited by boomtube; 12-01-2008 at 03:46 PM.
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Unread 12-01-2008, 05:22 PM
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Re: Case Cocentricity

I may load 62 cartridges, but most of my eccentricity measurements through the reloading process are with .223.

I think the error of the expander ball is mostly driven by the shell holder asymmetry.
The shorter and wider the case, the worse.
The longer and narrower the case, the better.

The 2moa figures are from 30 caliber data collected and math derivation by A.A. Abbatiello, the army, and NRA in an article about bullet tilt.
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Unread 12-01-2008, 09:40 PM
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Re: Case Cocentricity

I agree with boomtube and JE Custom

The Lee Collet Neck Sizer will solve most of your runout problems and is the easiest fix. The mandrel is free floating so when you raise your fire formed case up into the die, the mandrel does not push the neck to one side or the other and will center in the neck when the collets close on it.

The little runout that is left is reduced further by outside neck turning on new cases. I use the Bersin tool that not only measures runout but can actually correct it

and have found that the loads with the least runout and the easiest to fix were those that I outside neck turned and neck sized with the Lee Collet for my custom tight necked chambers.

Another factor is the softness of the necks. New cases or cases that have been recently annealed are easy to push from side to side in the Bersin and can actually be pushed out of concentricity by hand. Those that had been fired 3 or 4 times were harder to push from side to side but would stay there and the runout could be eliminated.

For the standard reloader I would say that by switching to the Lee Collet Neck Sizers you could forget about concentricity and just worry about reloading and shooting. For the more anal among us, then neck turning and runout correction are the next steps.
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Unread 12-01-2008, 10:43 PM
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Re: Case Cocentricity

"The 2moa figures are from 30 caliber data collected and math derivation by A.A. Abbatiello, the army, and NRA in an article about bullet tilt."

I have read the NRA and Lyman data but not Mr. Abbatteillo's or the Army's. Have never seen anything that put a fixed runout figure (.004") on the use of an expander ball. Based on my own experience, I really doubt its validity.

I agree with Woods that brass hardness comes into play but didn't want to write a book!
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Unread 12-01-2008, 11:06 PM
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Re: Case Cocentricity

Per the NRA and US Army in the A A Abbatiello 1960 article "Gauging bullet tilt", match ammo is most likely to be .002", while service ammo is likely to be .0025".
For a 1 in 10" twist 30-06, the math and the experiment agree .001" causing .55" extra group size continuing to .004" causing 2.2" extra group size. Beyond that, the chamber bends the cartridge straight.

"The NRA Handloader's Guide" 1969, a compilation from "The American Rifleman" 1950 to 1968, article gauging bullet tilt, by A.A. Abbatiello and was based on "The Bullet's Flight" by Dr F.W. Mann and the work of George L. Jacobson of the Frankford Arsenal in 1959:
"Mathematical Solution
The laterally displaced center of gravity moves though the bore in a helical (screw) path. The pitch of this helix is the pitch of the rifling, and the radius is the lateral displacement of the center of gravity. On leaving the muzzle the center of gravity continues in the direction it had at that point. .. The angle of emergence is that angle who's tangent is 2pi times the lateral displacement times the pitch. For a .004" displacement and a 10" rifling pitch, the tangent is 1/8 (2 pi)(.004) / 10 and the corresponding angle is 1.1 minutes.

...The effects which Jacobson found.. are essentially in agreement with the work reported here."

I built an assembly to straighten out necks bent by Redding bushing dies.
I reamed out the neck of a Forster sizer die to take a stepped mandrel.
The bent brass is inserted in the sizer die with a press and held tightly at the shoulder.
The mandrel in inserted into the top of the die with a mallet.
This over sizes the neck, but concentricly.
The brass can then be sized in a honed neck sizing die.

I have a friend with a collection of eccentric Lee sizing dies that have runout and orientation marked.
He measures and marks the runout in a piece of brass.
He chooses an eccentric die and sizes with the orientation of the die error opposite the brass error.

What does it all mean?
You can make gizmos to straighten brass, or fire form it in a concentric chamber.

Last edited by Clark; 12-01-2008 at 11:21 PM.
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Unread 12-02-2008, 01:40 AM
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Re: Case Cocentricity


Question for you (or anyone else using similar tooling) on the Bersin device: do you notice any issues w/ neck tension after 'correcting' a cartridge?

The reason I ask is on another forum (oriented around long range target shooting) people have theorized that in order to push the bullet over, that you must be kind of oblonging (not sure of a better term) the case neck - in short, ruining all the other work that goes into achieving consistent neck tension and release.

A couple friends of mine use the H&H tool, and swear by it - I just haven't quite made the leap yet. I haven't seen the Bersin around much, but noticed that Hornady just came out with such a device (check the video on their site for their case prep center... towards the end is a blurb for their concentricity tool) - curiously enough its marketing claims include something to the effect 'first tool of its kind to allow you to correct runout & concentricity in your ammo'. Guess they never looked very hard for the Bersin, H&H, or even some of the older concentricity gauges w/ holes in the base that you could insert and 'bend' (yikes!) the case straight.

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Unread 12-02-2008, 03:41 AM
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Re: Case Cocentricity

I disagree that one should not purchase a concentricity / run-out gauge. I just got mine recently and learnt a bunch. How do you know what's causing what and by how much if you don't measure it? Measurement is everything in accurate shooting - we measure groups after all, that's the ultimate test, but on the way there you need to measure most else I think.

I also agree that sometimes an expander ball is better. I started out getting what I thought was best and later discovered it wasn't necessarily BEST FOR MY PURPOSE. If you go really high-tech you need to sometimes be fitting in with the rest of the programme. like matching case neck wall thickness and chamber dimensions etc. I've posted an example below. In my case (thin case necks and SAAMI chamber specs) a Lee Collett die improved things above a Redding bushing die.

Not saying the Lee is better, but in my case at least it's more appropriate.

You could borrow a runout gauge instead of buying one, but I sincerely believe you need to have a way of measuring whilst you change variables and try different things to achieve the lowest run-out.

And yes, I still use Redding and even have some of their handgun dies.

Last edited by LRHWAL; 12-02-2008 at 03:45 AM. Reason: amplified
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