Concentricity:How much ?

[TnTom]

http://www.6mmbr.com/TacticalFroggyA1.html(www.6mmbr.com/TacticalFroggyA1.html)

Check out this link. He clears up a few things that can help get through the run out problem.

An area that's easy to ignore is the shoulder area and the importance in assuring it runs true.

The correct method of measuring depends on exactly what your trying to determine. (and I'm not sure what the NECO tool looks like) but:

The tool you are using is not an incorrect method of determining if the body diameter and neck outside diameter and bullet diameter are coaxial and that is the issue in part.

The tool you are using is probably the most correct of those I have seen on the market. I use a V-Block and indicator ( the indicator I use is not a drop indicator and allows me to access the neck id. I'll post a picture tomorrow.

It is not the method that can tell you if the neck diameters (i.d. and o.d.) are coaxial. (mine is yours isn't)

A drop indicator is really limited to outside measurement of o.d.'s (there are attachments to get to an inside diameter) but the wall or ball micrometer for wall thickness is our tool of choice. If the neck walls are not uniform the diameters are not coaxial. If the walls are not coaxial the bullet will not leave the case in line with the bore.

I have omitted mention of the shoulder diameter BUT if you can adjust your indicator so as to put the stem perpendicular to the shoulder then you could also check the shoulder coaxiality.

If it runs out chances are you will never have good bullet run out or runout tht you are looking for, like .001 or less . Read the link on 6br he talks directly to that relevance.

If the center line through the shoulder (cone) is not in line with the neck i.d the bullet will run out. SEE LINK he has nailed it.

 

[jmden]

Concentricity Gauges - Hornady Lock-N-Load Concentricity Gauge Hornady's new design...

You guys think this would work as advertisted?

Noticed that the Forster Co-Ax design apparently doesn't accept cartridges with OAL longer than 3.5"

 

[milanuk]

Bugholes from Bipod

Check this out. He clears up a few things that can help get through the runout problem.

Read it when it first came out; read it again just now. About the only major differences between his process and mine is I use a floating carbide expander ball, and my necks are squeaky clean (i.e. don't need to brush 'em) already. Since I have the same problem whether using a floating carbide ball in a Type 'S' F/L die or a Wilson neck die with *no* expander... that doesn't help much.

An area that's easy to ignore is the shoulder area and the importance in assuring it runs true.

Any hints... ?

The correct method depends on exactly what your trying to determine. (and I'm not sure what the NECO tool looks like) but:

NECO case gauge

The tool you are using is not an incorrect method of determining if the body diameter and neck outside diameter and bullet diameter are coaxial and that is the issue in part.

The tool you are using is probably the most correct of those I have seen on the market. I use a V-Block and indicator ( the indicator I use is not a drop indicator and allows me to access the neck id. I'll post a picture tomorrow.

Which one? I mentioned three different tools...

It is not the method that can tell you if the neck diameters (i.d. and o.d.) are coaxial. (mine is yours isn't)

If the necks have been turned with a quality tool such as K&M neck turner... how would the neck id and od *not* be coaxial? Are you talking about getting into inside neck *reaming*?

A drop indicator is really limited to outside measurement of o.d.'s (there are attachments to get to an inside diameter) but the wall or ball micrometer for wall thickness is our tool of choice. If the neck walls are not uniform the diameters are not coaxial. If the walls are not coaxial the bullet will not leave the case in line with the bore.

I presume by 'drop indicator' you are referring to something like the Sinclair test setups with the dial indicator 'dropping' straight down over the case/bullet? Again, my case necks are turned, so shouldn't they be 'coaxial'?

I have omitted mention of the shoulder diameter BUT if you can adjust your indicator so as to put the stem perpendicular to the shoulder then you could also check the shoulder coaxiality.

Probably doable with the NECO gauge.

If it runs out chances are you will never have good bullet run out or runout tht you are looking for, like .001 or less . Read the link on 6br he talks directly to that relevance.

If the center line through the shoulder (cone) is not in line with the neck i.d the bullet will run out. SEE LINK he has nailed it.

We must be looking at different links... the one I read (specifically the second page on reloading) only gives the most cursory overview of what he does or why.

 

[Bart B]

Tactical Froggy's info on that 6mm BR link pretty much duplicates what I've been doing since the late '60's. I lapped out the necks of a few RCBS .308 Win. standard full length sizing dies to .332" and another thousandth for each successive die; I've got full length dies with neck diameters ranging from .332 to .337 inch now. Depending on the loaded round's neck diameter, I'll use a die whose neck is 2 thousandths smaller that it. I set the die in the press to set the fired case shoulder back no more than 2 thousandths. This prolongs case life and helps ensure the neck is well cenered on the shoulder. No expander ball's used. Cases are deprimed and cleaned before lubing and sizing. I use a 50-50 mix of STP engine treatment and Hoppe's No. 9 bore cleaner for lube. I dribble a bit in a foam lined coffee can on a Thumler's Tumbler and lube 20 to 30 cases at a time. This puts a very thin but consistant film of lube on the cases. Case headspace after full length sizing is most uniform using this lube and method; spread's about 1.5 thousandth. I probably would get better uniformity if I used Redding shell holders that come in 2 thousanths steps in height over .125 inch.

Full length sizing should reduce body diameters no more than a couple thousandths. That is good and normal for minimum SAAMI chambers which I use. So the shoulder-body junction is now a bit smaller than the chamber at that point. No interference happens like neck only sized cases have when the case has expanded enough that it's sllight out of round now interferes with the chamber when the case shoulder's prefectly centered in the chamber shoulder.

When a rimless bottleneck round's chambered, it bears against the chamber wall at its pressure ring 'cause the extractor pushes it there. Bolts with spring loaded ejectors in the bolt face push the round forward until its shoulder mates with the chamber shoulder; this part is centered in the chamber. It' even more centered when the firing pin smacks the case setting the shoulder back a few thousandths.

It doesn't matter how much clearance there is around the neck. My chamber necks are .344 to .345 inch and even with .334 inch diameter loaded round necks, they're well centered. If the neck ain't centered on the shoulder, even tight chamber necks won't help; the neck will still be off center in the chamber.

Putting the case through a nylon washer that bears mid point on the shoulder contacting it all the way around its circumference and resting the pressure ring between two ball bearings more or less sets up a datum line between center of the case mid point at the shoulder and center of the case at the pressure ring. The dial indicator is 1/10th inch back from the bullet tip to measure loaded round runout. A sized (or fired) case can be checked the same way with the dial indicator just behind the case mouth to check neck runout Both uses are based on the same datum or reference line.

As the shoulder's mid point circumference and pressure ring are the two contact points of the case against the chamber when it's fired, it seems right to me that they should be the basis for checking bullet runout.

 

[TnTom]

bart I agree, the datuming you describe if I understand you are including the shoulder and a point on the body diameter would create a C/L line most accurately thru the case that would be the most accurate method to establish datum C/L.

Milanuk,

I would modify the set up and try to use a dia near the rim but not on it and possibly a ring on the shoulder. It would take some fabing to include the shoulder as part of the alignment as bart is referencing then it would be an excellent tool.

If you you use two circle on the body to locate the case not including the rim it would still align accurately and you could indicate the shoulder.

If the neck is turned it would be concentric. No reaming. I was referring to indicating the neck id before a bullet is seated when I said getting inside, not reaming.

I was thinking you were using a something like the sinclair.

I don't think the Hornady that uses a point on the ogive and the rim is a great setup.

I've looked at so many in the last few days I need to go back and get them straight.

The neco I think has too large of a bearing surface ( the 2 V's) though moving the case off the rim might be an improvement.

 

[milanuk]

The NECO has several different possible configurations... the knife-edge vee-blocks are re-positionable, and there is a nose-cone for supporting the cartridge via the tip of the bullet, and a special chord for reaching inside a fired case to measure wall concentricity, etc. I don't have the manual for it handy, but I don't think the picture shown (stock picture off the vendor's website) is actually the configuration recommended in the instructions for doing loaded round TIR. I'll have to check when I get home this afternoon (headed to a 500yd F-Class match).

 

[TnTom]

i don't think any of the commercial R/O fixtures use the shoulder to set up the datum but they all should, do they?

I haven't but will make the bushings for my v-block to get on the shoulder correctly. I appreciate your pointing that out.

 

[Mikecr]

Monte's setup(NECO) is sound and will show all runout. The only part of the shown measurement method that's incorrect, is the lack of case stop(possibly not shown for the picture). Without a stop the case could move fore & aft, and of course, this would introduce erroneous runout.
The Sinclair:


Bart I'm not following your extractor influence on a chambered round. A proper extractor for the case will not.
Now a button ejector, is bad news. I delete this on every bolt right up front by clipping the ejector spring for neutral positioning, or ordering the bolt no-eject, and/or the action with standing blade ejection.
If this leaves me with no ejection, I pick the rounds.
No problem as all my guns are made single shot anyway, and I can't tolerate my brass ejecting uncontrolled off the bench or into the grass.

The Hornady linked to is a 'concentricity gauge', and does not show most runout. These case benders/re-seaters adjust bullet seating as assumed the only issue.
They discount runout, as Bart has been all along.

Runout is not a contest (for lowest). If your gun shoots well with high runout, then there is obviously nothing to conceal about that. But it doesn't mean runout should be universally discounted(as implied with Sierra's sloppy reloading).
The thread is about standards & terms, and not what anyone can or can't get away with -in competition.

My contention is that ammo low in TIR is concentric and as straight as it gets, and that purely 'concentric' ammo may or may not be staight. Therefore, I choose TIR as my measurement standard even though it is far more difficult a pill to swallow.
I challenge you to prove me wrong -through actual measurement.

 

[Bart B]

Mikecr comments:

Bart I'm not following your extractor influence on a chambered round. A proper extractor for the case will not.
Now a button ejector, is bad news. I delete this on every bolt right up front by clipping the ejector spring for neutral positioning, or ordering the bolt no-eject, and/or the action with standing blade ejection.

All extractors push the case head sideways on the bolt face. At least the ones on Winchesters, Remington's, Garands, Paramounts, Springfields, Mausers, Rugers and others do. If they didn't, the case would slip out of the bolt face when the case is held in the bolt with the bolt removed from the rifle. Even with bolts with plunger ejectors removed, the case will be held against the bolt face edge opposite the extractor. I've sliped sized and new cases in a removed bolt's face, marked the back of the bullet with a dye, then chamberd them. All of 'em show scratches where opposite the ejector; evidence to me the ejector's pushing them there.

No way does the back end of the case rest on the chamber bottom from gravity as is oft times claimed. The only way the back end of a case will be perfectly centered in the chamber's back end is when the diameters of both are the same at the pressure ring area. Typically, the case is a thousandth or more smaller at that point.

What's a "proper" extractor's requirements?

I've removed plunger (button?) ejectors or cut their springs back too; good idea if you want to keep your brass clean.

 

[Mikecr]

All extractors push the case head sideways on the bolt face. At least the ones on Winchesters, Remington's, Garands, Paramounts, Springfields, Mausers, Rugers and others do. If they didn't, the case would slip out of the bolt face when the case is held in the bolt with the bolt removed from the rifle. Even with bolts with plunger ejectors removed, the case will be held against the bolt face edge opposite the extractor.

Well, you reference actions I don't use, but none of mine do this. There is no sideways force against the case head from my extractors. Zero.
I'm currently using BAT RS, BAT SVs, Tubb2000, Browning, and Cooper.
On these, once the case head snaps past the extractor to the bolt face, the extractor claw fits within the extractor groove without contact with the rim, and I can wiggle the case about the boltfaces without interference.
Of course the case is held on a removed bolt -provided the claw is on the topside. but turn the bolt 180degs, and every case falls off cleanly(for ejection).
If this isn't happening for you, then I suggest your extractors need facing.
They should not in any way interfere with the chambered cartridge.

My typical claw extractor, this bolt using standing blade ejection :


Case hanging with extractor at ~0deg:


Case hanging with extractor at ~270deg:


Right at 180deg case falls off face:


Now before assuring me that you've successfully competed for years with bolts having a deathgrip on cases; Consider how well you MIGHT have done otherwise..
This is a BAT boltface. Currently the winningest configuration in both point blank and LR BR.

 

[Moman]

JE, with your permission, I would like to delve a little more into neck turning and how it may effect runout/concentricity. I think what I'm after will stay on topic.

How many of the posters up to this point neck turn their cases?

I ask because in the past I have settled for .001 neck wall variance and have been happy with that number. I have had trouble with this last lot of brass in that neck wall variance is anywhere from .001 to .005. The majority of the cases are .003. Runout on these loads it gynormous.

How much of a difference would it make if I were to neck turn these cases to .001 variance or less? How much would this help with runout?

 

[Bart B]

I think one thousandths spread in neck wall thickness is fine. There's too many other things that'll open up ones groups at any range to make a difference in cartridges burning more than 40 grains of powder.

Nor do I think a "death grip" of extractors hurt accuracy either. The difference in a death grip and none at all will only change the location of the back end of the case a couple thousandths at most. Not enough to make a difference in my opinion. The smallest 15+ shot groups I know of past 300 yards have all been shot with rifles with such force at right angles to the case/chamber axis.

Here's some examples of what such neck wall variance and death grip extractors will do at 800 and 1000 yards when bullet runout's no more than 2 thousandths:

First, 20 shots from a .308 Win. 30-inch Kreiger barrel in a Paramount 4-lug action using WCC60 unpreped full-length sized cases with a Sierra 155-gr. Palma bullet; number 1 and 2 were the first two shots from a cold barrel after two sighters:

Second, my plot from testing a new Kreiger barrel in my Model 70 long range rifle. .30-.338 Keele (.300 Win. Mag. case run through .30-.338 full length sizing die) unprepped cases. Top 15 black dots are impacts from once fired, full length sized cases shooting Sierra 190's. Bottom 15 red dots from new full length sized cases shooting Sierra 200's. All HPMK bullets were shot alternatly, one 190 then one 200; all 30 shots fired about 20 to 25 seconds apart after two sighting shots were fired to zero. That X-ring's 10 inches in diameter.

I thought it was interesting that two loads shot so close together.

 

[J E Custom]

JE, with your permission, I would like to delve a little more into neck turning and how it may effect runout/concentricity. I think what I'm after will stay on topic.

How many of the posters up to this point neck turn their cases?

I ask because in the past I have settled for .001 neck wall variance and have been happy with that number. I have had trouble with this last lot of brass in that neck wall variance is anywhere from .001 to .005. The majority of the cases are .003. Runout on these loads it gynormous.

How much of a difference would it make if I were to neck turn these cases to .001 variance or less? How much would this help with runout?

Moman.

You don't need my permission to bring up points of interest to this post. That's why I post
anything. to get different opinions.

I will give you my opinions on your questions and leave it at that.

First I will say that perfection may not be nessary because I do not know how to measure
the difference between a case that has .001 wall thickness and one that has .0005 so I just
try to make them as good as I can.

With my old neck turner .001 was about the best I could do ( And I did fine but wanted better)
so I bought a better neck turner (More precision and adjustable down to the 10 thousandths
and it did improve the consistency in neck thickness.

Next = the improvement in concentricity was phenomenal when I first turned the necks and then
sized the brass before fire forming the finished brass has almost no concentricity issues or
run out. All I can deduct from this is that with true neck thicknesses the neck is not pushed off by an uneven wall thickness and sizes more uniform , and when fire formed it is near perfect.

Again as I said I'm not sure how much difference it makes but it makes me feel better knowing
that I have the best ammo I can load. so that if an issue shows up I can look somewhere else
for the problem.

I do know that the more concentric the ammo is the better the groups and Standard deviations
Will be.

So for precision shooting and testing ,I turn all of my necks in this way. Later I may decide on
some applications that the difference In a .100 thousandths group and a .250 is not worth
the effort but I know what the rifle is capabable of.

I hope you get a lot of responses !

Just My 2 cents

J E CUSTOM

 

[TnTom]

AS JE pointed out to gage the difference between .001 and .0005 wall thickness could get a little hard to determine, and you gotta draw the line somewhere.

I think there is sometimes over emphasis on the run out issue when so many other variables enter into good groups but it still it cant be ignored.

Minimizing the bullet press force I have found helps me to keep r/o minimal and I do that by making sure my cases are properly annelled and interfernce is between than .0015 and .002.

I have found that the neck seems to get a little kinked when work hardening is present and can make the bullet harder to press especially if the interference become .003" or more. It doesnt take much in the area of the neck being slightly tweeked or deformed to exaggerate the r/o. If the necks are pliable, clean and the walls are relatively uniform the bullet slips in smoothly and its measurable when chronographing and grouping. I get my most uniform loads when I assure those 3 things occur during my reloading..

...and as far as wall thickness goes I'm not spending more tha a moment to assure myself its not getting greater than .001 /.0015 or so as thats as close as you can measure with a degree of accuracy without getting into mics than have a resolution into the .0001 - .0005 or greater range and thats really getting expensive (for many of us). You can do it with a dial indicator and mandrel but still the indicator needs a resolution of 10 to 1 to resolve measurement less than .001" and most indicator I see on reloading benchs run in the .001" resolution increment. I have indicators that resolve to .00005 but there very sensitive and almost usless in reloading.

If your instrument reports in .001" increments you can feel confident of reading between the .001 and .002" range.

I suggest turning or dusting off if it appears that your getting around .002 and greater and you do not have to have a 360 deg cleaning when turning of the surface to to move a .003" wall thickness to .0015.