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Concentricity:How much ?

 
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  #22  
Old 02-11-2010, 04:22 PM
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Re: Concentricity:How much ?

"Sierra Bullets has been full length sizing their cases used to test their bullets for accuracy since the 1950's; I don't think anybody shoots 'em as accurate as they do. Sierra doesn't even work up loads nor weigh charges."

Appreciate the thought there, and you're absolutely correct about how they do their reloading in the range. Having sent about 20 tons of bullets downrange there over the past 20+ years, yeah, full length sizing only.

Kevin Thomas
Lapua USA
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  #23  
Old 02-11-2010, 04:51 PM
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Re: Concentricity:How much ?

Kevin, thanks for confirming what I thought was your former employer.

Martin Hull was instrumental in telling/showing me how to reload very accurate ammo. I shot a lot of matches with him. He'll be missed; bless his departed soul.
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  #24  
Old 02-11-2010, 04:57 PM
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Re: Concentricity:How much ?

I worked in quality assurance for about 40 years and the lack of understanding regarding the relationship of center line is profound.

The best reference is A.N.S.I 14.5 Geometric Tolerancing and Dimensioning (1982). This standard gives in details the foundation for examining the elements of all geometries.

Straightness, roundness, runout, total indicator reading (tir), and concentricity are conditions that are reflected in cylindrical geometries.

It would benefit anyone who delves into this topic to read this standard.

Most of the devices I have seen sold in the shooting industry to measure "concentricity" are not. I have seen only one instrument or "jig" that sets up the case to measure concentricity reporting the relationship of the neck i.d and o.d and exposes variation of the wall thickness which is the shift of center line between the datum i.d. and the o.d.

The concept that concentricity is 1/2 of the C/L deviation is somewhat correct. It would take a shift in center line equal to 1/2 the indicator reading to align center lines.

The other tools as others have expressed in this thread are measuring straightness or lack of in the assembly caused by any number of conditions, like eccentric neck i.d./o.d. conditions (wall thickness), eccentric body diameter combined with eccentric neck i.d/o.d.

Keep in mind the term "datum". It is the point ALL MEASURMENT is TAKEN FROM.

Notice that the tools sold on the market Hornady, Sinclair, Lyman etc almost all have tools each using a different "DATUM".

Sinclair "Datums" or locates on the case body diameter, Hornady "Datums" on both ends of the assembly - the ogive at one end and the base at the other. Lyman "Datums" on the neck i.d. using a mandral and it reports the neck concentricity and wall thickness variation and is in my opinion the most useful reference point.

Before you can reduce TIR to zero the neck i.d, o.d., case body and bullet must share the same centerline. If the neck walls are not uniform neither are the neck centerlines and when checked with a tool that is reflecting straighness and .0005" shows up you can be certain that there is at least that much off centerline somewhere. Can a value of .0005 show up if a neck C/L is .001' excentric...yes but there is masking element playing into it all. It would depend on how the assembly is being "Datumed"

This is a long long subject and to try and delve into all the aspects would require something like the ANSI standard for cylindricity. Check it out.

Also I find much of the TIR that is in question derives from the should area getting kinked in F/L sizing of work hardened cases. I get my best results assuring the neck walls are uniform sharing the same center line, F/L sizing only when the brass flow indicates it time other wise I let the chamber establish uniform center lines when fire formed then turn if needed neck size followed by annealing.

I have seen many F/L sizing dies that do not run true, the forming cylinders center lines are not consentric. Check yours out with a v-block and appropriate indicator. Also presses can influence C/L lack of uniformity if the ram and die threads are not in line or the die threads are skewed off center (happens during the manufacturing process and it does happen, cast iron especially.

I did some extensive measuring for Remington years ago and be sure that new brass is not in the condition we like to think it is. Brass and bullet dies. Bullet die center lines are at times not square to their mounting surface and that's a problem.

The most straight forward tools to measure C/L relationships for what we try to understand in reloading is a VBlock and .0005" dial indicator.

If I can keep all my loads about .0015" or better i'm happy but I have no problem with .002". When I see that value showing up I know that my brass is getting toward the end of its life probably work hardened and that the necks walls are about at their limits for turning. Usually its in the shoulder area and maybe bumping can get it back into good form maybe not. Its probably time to chuck it.

If you get a chance Read A.N.S.I 14.5 Geometric Tolerancing and Dimensioning. Its what manufacturing uses as THE guide for measurement or metrology , the building jigs and fixtures, establishing correctly illustrated blueprints nad so everyone can speak the same language.
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Last edited by TnTom; 02-11-2010 at 05:31 PM.
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  #25  
Old 02-11-2010, 05:42 PM
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Re: Concentricity:How much ?

TnTom, your info is impeccable. Kudos to you for sharing it.

Best example of such things regarding good new cases to begin with and how they're treated before putting components in them happened in 1991. I and a few other former Palma team members were given a thousand Sierra's 30 caliber 155-gr. prototype Palma bullets to develop a load for. The end result would be used to make several thousand rounds of ammo for the 1992 World Championships.

Winchester had to retool and reset case forming dies in their production line a few times. But they finally got fairly uniform cases made for us to use. Two Dillon 1050 progressives were set up to load the ammo. First one ran a Lyman neck expander in each case to uniform its mouth dimensions and also seat Federal 210M primers in them. The second 1050 auto metered 45.3 grains of IMR4895 and seated a 155 in each case. Charge weight had a 3/10ths grain spread and bullet runout was 4thousandths max; typically between 2 and 3 thousandths.

20 rounds were taken at random and tested in a Win. 70 based Palma rifle clamped in a machine rest. They shot inside 2.8 inches at 600 yards. Not too shabby for new cases in a short throat SAAMI chamber. Folks from around the world used the ammo in a big match at Raton in 1991 and reported about 1/2 MOA accuracy at 600 yards; and better than 1 MOA at 1000.

Last edited by Bart B; 02-12-2010 at 06:37 AM.
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  #26  
Old 02-11-2010, 09:34 PM
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Re: Concentricity:How much ?

Bart that study had to be a lot of fun . Anopportunity to put together some very valuable information. The sample size really establishes credibility.
You put to rest a lot of speculation regarding how much is too much whether related to powder measure, bullet r/o, basically the whole tamale. I would have loved to see all the data.

Great job.

I enjoy measuring so I may over indulge. I retired recently and miss a lot of it. I did a great deal of process improvement type of activities applying the rules of measurement and a lot of statistical process control. Now its just directed toward a hobby I enjoy but still rewarding. The problem solving part of reloading is fun especialy when the results are like what you experienced. Must of been a thrill.

As elusive as the elements are in reloading the frustration from not having the tools to work with or working with tools that mislead has to take its tolls. It becomes labor intensive and discouraging for many. Thats another issue.

In r/o its a matter of placing all center lines in the same plane.

Do you still shoot in Palma events?
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Last edited by TnTom; 02-11-2010 at 09:49 PM.
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  #27  
Old 02-12-2010, 12:16 AM
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Re: Concentricity:How much ?

Thanks to every one that posted on this thread !!!!!

I think I am on the right track and must be doing OK (But there is always room for
improvement).

I have checked every way and every location trying to do as TnTom stated: "It's just a matter
of placeing all center lines on the same plane" and found that everything effects the final
outcome and must taken in consideration if quality ammo is to be loaded.

And I feel even though there is no definitive solution, All the things mentioned have helped
to improve the process and the accuracy.

I hope this thread remains active and more experience and opinions are shared with all of us.

Thanks again

J E CUSTOM
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  #28  
Old 02-12-2010, 08:35 PM
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Re: Concentricity:How much ?

okay... I'll throw this out there for those of you getting really small runout numbers...

I have an older Sinclair vee-block setup, one of the newer ball-bearing units, and a NECO setup.

I saw where someone (Tom?) mentioned that different gauges reference off different points - the vee-block and ball-bearing units depend on the case body below the shoulder being perfectly concentric, and may give a very different reading than ones like the NECO where the round may be supported by just the bullet and the case above the extractor groove. This mirrors my own observations.

The question is... which one is 'right'?

I've been somewhat frustrated with this issue over the years, as I've never been able to get the super-low TIR values that I see discussed on the 'Net. Not consistently, anyways. In general, my loading equipment is about as good as it can be short of getting custom dies cut to match fired cases from my chambers, etc. I've used Forster, Redding, RCBS, Dillon, Harrell's & Hart presses, Forster, Redding & Wilson dies, quality components, done neck sizing, F/L sizing, variations of both, etc. and so on. If I went scrapping rounds that measure over 0.003" runout, I wouldn't have hardly anything left to shoot. Doesn't seem to matter what gun they come from, what caliber, what die or press is used...

Actually, 'frustrated' doesn't begin to cover it. Then again, the bullets tend to go where I point them, so I take a limited amount of consolation in that

Monte
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