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Concentricity:How much ?

 
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  #36  
Old 02-13-2010, 03:34 PM
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Re: Concentricity:How much ?

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.
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  #37  
Old 02-14-2010, 09:36 AM
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Re: Concentricity:How much ?

Mikecr comments:
Quote:
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.

Last edited by Bart B; 02-14-2010 at 12:07 PM.
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  #38  
Old 02-14-2010, 09:16 PM
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Re: Concentricity:How much ?

Quote:
Originally Posted by Bart B View Post
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.
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  #39  
Old 02-14-2010, 09:35 PM
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Re: Concentricity:How much ?

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?
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  #40  
Old 02-15-2010, 09:47 AM
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Re: Concentricity:How much ?

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.

Last edited by Bart B; 02-15-2010 at 12:20 PM.
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  #41  
Old 02-15-2010, 11:18 AM
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Re: Concentricity:How much ?

Quote:
Originally Posted by Moman View Post
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
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  #42  
Old 02-15-2010, 01:30 PM
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Re: Concentricity:How much ?

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.
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