Concentricity:How much ?

[jmden]

Interesting thread.

This is what I do and I'm sure some of you more expereinced will have some ideas one way or the other:

1-pick up 300RUM cases where I can inspect each case before purchase-can't be completely sure they are from the same lot, but most likely are--each case is inspected for centered primer/flashhole, flashole inspected from both sides and from inside checked to make sure no obstructions and properly factory deburred, neck reasonably round, any other visual anomolies noted and dealt with

2-anneal case mouth/shoulder--I know I've heard that they are supposed to be annealed from the factory, but I don't see the look of the 338 Lap, for instance and i'm not sure how much I would trust the annealing job of most American made brass anyway--just trying to treat every case as consistently as possible

3-trim to length I've decided on based on measured chamber length--chamfer and debur

4-I don't sort these cases by weight and don't sort them at all other than that mentioned in step one--did a bunch of testing a few years ago prompted by a member that used to post here alot years ago from AK (Brent, I think) that he'd found that the case volume had little to do with the case weight on these 300RUM cases and that the case volumes were remarkably consistent regardless of case weight differences--I found the same so I don't weigh these anymore

5-run 'em through the matched Sinclair mandrel for the Sinclair neck turning tool and then neck turn to take off approx. 75-80%

6-run through the Redding FL die with .008 competition shellholder (to fit the chamber more closely and reduce the amount of brass being worked)

Edit: just trying to get the case as straigt as possible so that the first firing might potentially be used to start to get an accurate load development process going. Some of these cases do look straighter/better to me after doing this and it seems to have provided more consistent results with fireforming loads. Could be wrong--lots of variables.

7-fireform

This usually leave me with less than .001 runout on the Sinclair concentricity guage. Edit: ...after reloading again, that is. Bullet and case neck runout is typically held to less than .001 AND I have gone back to used the regular FL dies with button expander. Big no no, I know, but I get straighter cases than when I've tried 2 different bushing dies. There's several keys here, I think, two of which are to let your shell holder float (nothing retains mine) and let your button expander float but soft seating the adj. nut against and o-ring. This lets the expander find it's own center--the center the die just made on the case. Use Imperial Sizing wax as well--have yet to find anything that does as well as this stuff. Just whst seems to work well for me. I seat .010 from the lands with 210 Berger and have been getting very consistent precision from this factory rifle, but there's alot of work that has gone into improving the entire system (including my shooting form), so it's difficult to pinpoint any one area. Lots of little things might add up.

 

[J E Custom]

Why on earth would you 'restrain' what you're trying to measure?
You're masking variance. This is why your numbers are so low.
Sounds like you're using a concentricity gage rather than a Runout gage.

As a note, the Sinclair 'Concentricity' gage is actually a 'Runout' gage.

Why are you guys FL sizing NEW brass & culling by runout?
New brass could measure any runout, even if turned, until it has been fire-formed into it's final product.

#1 Stop FL sizing new brass. It is wasted time.
#2 To see your brass at it's lowest runout(it's best potential), measure it after fireforming, & before doing anything to it.
#3 Measure after each sizing stage to see the specific runout contributor
#4 Measure loaded runout off the ogive at a point near land contact, with the bullet unrestrained. Don't assume anything about the neck, or even think about it at this point.
Think TIR off the ogives.

That's why I posted this question : to get some different approaches to the problem.

And it brings up some interesting questions=

When I think of Concentricity I think of every thing on the same center line from one to
the other.

When I check a barrel for run out I place it between centers and gauge from end to end
(This tells me if the barrel is strait)

When aligning a set of scope rings I use a bar or a lap. (The pointer type can match at
the points and still not be aligned strait for the scope.

So when I check the finished round for concentricity I want it to be absolutely strait from
the tip of the bullet to the base of the case (On the same center line). I have checked
the cases and they were near perfect but when I check the bullet ogive it would be off
quite a bit(Pointing away from the center line) .

This made me improve the bullet seating process ,and Like you after the case has been
fired in a good chamber it is about as good as it gets. so the problems seamed to be in
the sizing and bullet seating.

Now if I do both processes (Concentricity and run out) I find that I can detect a problem
and fix it easier and don,t have to guess where the problem is.

The dimensions I am getting are the worst reading I can get no mater where I gauge them
and the method I use.

And your question about case prep befor fire forming is also a good one. I simply do it to
minimize fore forming (If it is good why fire form it just use it to hunt with and fire form at
the same time.

If this is the wrong way to achieve the minimum run out and the best concentricity please
guide me in the right directions.

More input please And thanks for your reply

J E CUSTOM

 

[Mikecr]

If your chambers are anything but **** round, cartridge runout is by far the least of your concerns.
Also, dies don't remove runout. They cycle brass to cause it.
Don't believe me? Measure runout on cases freshly pulled from a smoking chamber. Then measure it after a cycle with your dies.
I don't care how perfect your dies, even those that contribute nothing to runout, they still cannot REDUCE runout. This is because the devil's in your brass.

But you can manage this to the point of irrelevance right from the git-go.
This is how:
1. Cull plenty of brass by thickness variance in each neck, as measured with a properly set up ball mic. Settle for well under 1/2thou variance, 360deg, and rake the rest in a trash can. Don't think turning negates the need for this. It doesn't.
2. Prep brass, partial neck size, and fire-form.
3. [optional]Check H20 capacity, and what leaves your tolerance is again raked in the trash.
4. Workout each stage of sizing and seating to produce runout as low as desired.
(for some, lowest measurable).

With this & depending on your load pressures, spot checks for runout every few reloads should get it. Runout always grows, a little bit, with every cycling of the brass. But my brass will wear out many barrels before runout is a concern.
And that is why I use the process described.

 

[Buffalobob]

I shoot a lot of over bore magnums. A couple of them will only give one firing per case. Fireforming may not be an option and I do not waste barrel life on it. I will prep the unfired cases and may full length size them if I think the runout on the neck is bad.

I weigh bullets and cases and cull by weight. I have experimented with weighing cases at F-class and at 1000 yards a case that is different will shoot different. I marked every case one day that gave me a flyer and reloaded them for the next competition and they gave me flyers again. A bad case is a bad case so get rid of it.

 

[Bart B]

Hey guys,

I have a slight problem with threads like this, in that I'm not sure we're all speaking the same language. Everyone seems to have their own methods of measuring run-out, and they're not all the same. Saw this sort of thing constantly in the QC range, with customer complaints of concentricity issues. The vast majority would turn out to be customer errors in how they were measuring what they thought was run-out.

I'd like to see some sort of standardization on how we measure, so that all our results would corelate to one another in a more meaningful manner. Don't ask me how we do that, but that's what I'd like to see.

Beyond that, I think we can all agree, less is better. But how much?

Great comments. I totally agree.

I've been facinated/measuring/testing/wondering about bullet runout for years. Even made a few tools to measure it. Depending on how the round was supported and where the dial indicator's plunger was put, different numbers would show up for the same round. And a .223 Rem. with its bullet 2/10ths of a degree crooked to the case axis will show less runout than a .300 Wby. Mag. with its bullet at the same angle.

As rimless bottleneck cases are pressed hard into the chamber shoulder when fired (firing pin impact does this with enough force to set the case shoulder back a few thousandths), that very well centers the front of the case in the chamber. And the back end's pressed against the chamber wall (typically at the pressure ring) by the extractor's force on the case head. With bolts having inline plunger ejectors, cases are pushed forward against the chamber shoulder, too. Which means every case is a tiny bit crooked in the chamber when it's fired. If a round's got absolute zero runout, its bullet will still be a tiny bit crooked to the bore axis. Doesn't matter how much case neck or bullet clearance to the barrel there is. The front of the round's centered this way in the chamber. If one wants the bullet to be aligned with the bore, the case neck needs to be well centered on the case shoulder. It doesn't matter how much clearance there is between the shoulder-body junction and the same point in the chamber, but there can be no interference at this point.

As there's not such thing as a perfectly round case, their slight out of round numbers will effect runout numbers

So I made a tool out of ball bearings on Garand cleaning rod sections held in aluminum blocks at the ends. That let the loaded round rest at its pressure ring and mid point on the shoulder. Put the dial indicator on the bullet 1/10th inch back from the tip. If I put the dial indicator just back of the case mouth, I can measure case neck runout. Whatever runout there is on this tool will pretty much match what there is when the round's chambered. And any slight out of round the case is at its body-shoulder junction won't effect the numbers.

In measuring case neck runout with several rimless bottleneck and belted cases, then using all sorts of bullet seaters (standard, inline chamber types, cheap, expensive), they all seated bullets very well inline with the case neck. And the case neck still had the same amount of runout after bullet seating as it did afterwords. Which tells me that if the case neck axis ain't in line with the case body, any bullet seating tool's not going to help. Something has to be done to make sized cases end up with straight necks. I noted on Redding's web site some time ago they've now got an article covering this very issue. It's at the "concentricity" link below:

concentricity

Here's what I've found helps make sized case necks as straight as possible. And produce best accuracy, too.

First, deprime (without sizing) fired cases then clean them before any sizing's done. I run fired case necks over a bore brush before this to clean out most of the powder fouling.

Use full length sizing dies with their necks lapped out to about 2 thousandths smaller than a loaded round's neck diameter and reduce fired case body diameters no more than 2 thousandths. This supports the case body very well when sizing the fired case neck down with minimum brass movement. There's no expander ball coming back up through the case neck that often bends it from where it was at coming out of the die's neck. Redding and RCBS make full length bushing dies that does the same thing. I've tried expensive and popular neck sizing dies (regular and bushing only types) that never produced sized case necks as straight as full length sizing dies with properly sized neck areas. I and others have got 40 to 60 reloads per .308 Win. cases using this method for maximum loads.

Every time I trim cases back to length, I debur the case mouth inside with an Easy Out screw extractor. It's got a better angle and doesn't leave as sharp an edge that scrapes off bullet jacket material when seating them. I run the case over that bore brush again to make the inside edge rounded facilitating minimum resistance to bullet seating.

It doesn't matter what type of seater I use, runout's typically 2 thousandths or less with varous 30 caliber cases. I've seen no improvement in accuracy through 1000 yards with any less runout on ammo shot in standard SAAMI dimensioned chambers.

 

[Mikecr]

a .223 Rem. with its bullet 2/10ths of a degree crooked to the case axis will show less runout than a .300 Wby. Mag. with its bullet at the same angle.

Not if the bullet angle is the ONLY source of runout.

let the loaded round rest at its pressure ring and mid point on the shoulder. Put the dial indicator on the bullet 1/10th inch back from the tip.,, any slight out of round the case is at its body-shoulder junction won't effect the numbers.

Won't affect YOUR numbers, but this frees mid-body and discounts it as a problem –by subtracting it from measure.
Many shooters are doing this(rationalizing/discounting runout) by jamming their bullets. And atleast several concentricity tools/case benders do the same, given that bullets are jammed into the lands, as they are in the tool.
Only the truth passes all tests.. So runout is not a problem to conceal, as straight ammo measures just that –no matter what.

Something has to be done to make sized cases end up with straight necks

It's called fire-forming,, the best way to straighten a case there is.
The only way to alter neck centerline after fire-forming is to FL size and/or expand necks away from centerline. If you do neither, your necks will remain centerline (although there could still be runout, that could still be an issue).

This is where partial neck sizing is a better plan. It preserves the trueness in necks that fire-forming produced. Full length sizing a neck can only alter trueness, and serves no positive purpose other than to reduce a wildcat neck to lower cal..
Expansion is required, but currently risky IMO because the operation is free from centerline (it could be off). And the worst contributor to runout ever invented is the button expander.
I currently top expand with Sinclair carbide mandrels(just before bullet seating) to drive any thickness variance outward. It is a free floating expansion, just like bullet seating, and could could alter centerline -if I had FL sized necks..
So far it has not contributed to runout off the noses, except to reduce it. Like said, and for me, seating is a very minor contributor to runout.

If you'll measure little runout from your brass fresh out of the chamber, then stop & consider the 3 ways you'll screw this up:
sizing, sizing, & sizing (in order).

 

[Bart B]

Mikecr, I've tried all sorts of partial necksizing. Used different full length sizing dies for both rimless and belted bottleneck cases. They all ended up pushing the fired case shoulder further forward that where it was. Bolts bound up to various degrees depending on how tight the partial neck sized case fit the chamber. Accuracy was not very good at all. Even tried expensive neck only dies using bushings of different diameters to size different amounts of the fired case neck. Again, poor accuracy.

Partial neck sizing with a full length die and neck only methods often produce better accuracy than full length sizing that sets the fired case shoulder back way too far. Most of the high power rifle matches (and records set with them) are won with full length sized cases. The smallest test groups at the longer ranges having more than 10 shots in them I know of have all been done with proper full length sized cases.

I and others get better accuracy with new cases than any partial or full neck sizing process of fired cases; especially with belted magnum cases. And in standard SAAMI dimensioned chambers, too. 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.

When partial neck sizing has a good track record in disciplines where best accuracy is attainable, I might try it again.

 

[Kevin Thomas]

"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

 

[Bart B]

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.

 

[TnTom]

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.

 

[Bart B]

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.

 

[TnTom]

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?

 

[J E Custom]

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

 

[milanuk]

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