Question about chasing concentricity. . .

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edwardware

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I'm reloading for a Rem 700 .223 bull barrel, and my latest rabbit trail is concentricity. It's always seemed that I had an uncontrolled variable somewhere causing good recipes (0.4-0.7" @ 100) to start throwing fliers. Over the course of a year, ~1000 reloads, 5 bullets, 2 powders, etc, I haven't found a recipe that's reliably under 1".

So I built a concentricity gauge, and lo and behold, my expander ball was pulling necks 0.004-0.008 off centerline, with seated bullet runout varying up to 0.010 at the leading edge of the bearing band. I bought a neck turning setup, polished the expander ball, and bought a Redding Competition Seater (ouch!). I've just finished the first batch: LC-13 brass, FL sized, outside neck turned necks to 0.011", annealed, FL resized to 0.002" tension, checked neck concentricity, and culled any over 0.001".

Now I've seated a couple bullets (in the Redding Comp Seat), and the eccentricity is back!

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Is it really normal that seating (in a Redding Comp Seater, no less) should double runout on the neck, and triple it on the bullet? What am I missing here? This was a lot of work for on a ~30% reduction in runout.
 
I think the sized case mouths end up too small. Seating bullets in them bends them a little.

Anytime the expander ball is polished its diameter is a hit less. I'd get a new one then try again.

Full length bushing dies with bushings .002" smaller than loaded round neck diameters and no expander ball will resize fired cases minimally and end up with straight necks and bullets with no more than 1% of caliber runout. That's .0022" for 22 caliber cartridges.
 
Polish the button, yes, and then you need to center the shaft as well.

Raise the ram so the case is fully inserted into the die, and now adjust the button down way past the neck so that it is not in contact with the neck or shoulder at all. Then while keeping the case fully raised, slowly thread the neck sizing button by turning the stem on the die until you just feel the button make contact with the shell neck, then lower it one full turn.

Now run a case up into the die fully, then slowly lower the case until the button just makes contact with the neck. Now reverse direction on the handle EVER SO SLIGHTLY just to remove the slop in the mechanical linkage, but don't even move the case, now TIGHTEN the lock ring on the decapping stem (which also holds the sizing button). This gets the sizing button as close as we can to being centered. It is not perfect, but it is as close as we are going to be able to get.
 
Full length bushing dies with bushings .002" smaller than loaded round neck diameters and no expander ball...

I second this, notice that Bart recommended no expander ball, that's exactly how I got the best runout numbers for my hand loads.
 
I think the sized case mouths end up too small. Seating bullets in them bends them a little.

Anytime the expander ball is polished its diameter is a hit less. I'd get a new one then try again.

I second this, notice that Bart recommended no expander ball, that's exactly how I got the best runout numbers for my hand loads.

I measure only 0.002" neck growth on seating (0.246 seated - 0.244 sized). Most of what I've read says 0.002-0.0035 is correct neck tension. Is that the case?

. . . Full length bushing dies with bushings .002" smaller than loaded round neck diameters and no expander ball will resize fired cases minimally and end up with straight necks and bullets with no more than 1% of caliber runout. That's .0022" for 22 caliber cartridges.

I understand the issue with expander balls, and I'm studying up on honing out the neck of this FL die to match neck-turned brass, but note that the concentricity of the sized cases (I also check the interior of the necks with a test indicator) was very good after the expander ball was put away. The eccentricity showed up upon seating.

So, necks are concentric (inside and outside) after sizing, but not after seating. I only very lightly chamfered the inside of the necks; do I need more chamfer? Did the annealing leave them too soft? Most importantly, is a 0.002-0.008" bullet eccentricity going to be noticeable in a factory-barreled rifle?
 
What brand of cases r u using?

Full-length resize, partial fl resize, or neck size?

Necks trimmed, or not?

Compare two different seating die results to eliminate a die problem.

Luck,

murf
 
So, necks are concentric (inside and outside) after sizing, but not after seating.
Brass problem like Redding has posted?
a.k.a Neck Runout With Bottleneck Cases

The concentricity, or neck runout, of loaded cartridges is an important consideration for reloaders and especially the varmint or target shooter.

There are many factors that can cause or contribute to neck runout during the reloading process and many reloaders who have not dealt with the problem before quickly blame the sizing or seating die.

While the dies may be at fault or have a contributing defect, modern CNC machinery and reamers that cut the body, shoulder, and neck simultaneously make such occurrences rare. Most problems are related to the brass itself and its uniformity both in terms of hardness and thickness and how much it is being stressed in the reloading process.

An entire book can be devoted to this subject, but the amount of stress the brass is subjected to can be your key to finding a problem. If you "feel" any difficulty and /or heavy resistance when resizing your cases this can be a telltale clue.

Excessive difficulty while resizing can indicate any of the following: Poor choice of case lube, failing to clean the die and/or brass, faulty polish inside die, chamber large or at maximum S.A.A.M.I. spec resulting in excessive brass resizing. A large neck diameter in the chamber combined with brass that is thin or excessively turned can cause crooked necks in a hurry. The more brass has to be moved the more its residual memory takes over.

Resistance to pulling your cases over the size button can indicate problems. A "squawk" says "shame on you", you forgot to brush the residue out of the necks. A hard drag can indicate that the top of the size button is not smooth. Don't be afraid to polish the top radius with #600 wet paper, but don't reduce the outside diameter or you can create an excessive bullet fit. Carbide size buttons are now an option also; they have a lower coeffecient of friction.

We have conducted many tests over the years on the various factors contributing to concentricity problems with bottleneck cases. We have repeatedly found a definite correlation between the uniformity of the brass (or lack of it) and the resulting concentricity of the neck to the body of the case.

An interesting experiment also revealed that neck turning of brass that was intentionally sorted as non-uniform, showed little or no concentricity improvement when used in standard S.A.A.M.I. spec chambers. Conversely brass that was sorted and selected for uniformity remained uniform and concentric with or without a neck turning operation.

Another interesting observation can be found in the examination of fired cases that have crooked necks "as fired" right out of the chamber. Usually the chamber is being blamed for the problem.

Looking at the primers under magnification you can usually find a telltale machining mark or other blemish that was imprinted from the bolt face. This will give you an index mark with reference to the chamber. Mark this index mark on the cases with a felt tip marker and go about checking the concentricity. If the runout is random to your index marks the problem is not the chamber. Further examination will show the same correlation with the good and bad brass.

Note that to this point we have not talked about seating dies. That is because 98% of all concentricity problems exist in the brass prior to bullet seating.

Keep in mind that no seating die ever made will correct problems. The best you can do is to obtain a quality seating die that does not add any.
You may want to buy another gauge to check your gauge. :D

Test on target, forget the gauge.
 
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Certain cases will always seat straight bullets crooked. Mark each case head with a sharpie as to cartridge run out ( in thousandths) with one slash Mark for each thou out of round. You should find, after a few reloads, that certain cases always have "good" runout, and certain cases always have "bad" run out.

r u - are you

murf
 
There are some misconceptions about honing die necks, case neck wall thickness and axis, and how case necks/mouths interact with bullets seated in them.

If a die neck is honed out to a larger diameter, it must be done on the die chamber axis else the new neck axis will not be aligned with the die shoulder and body axis. It's best done one of two ways. Best way is to chuck the die in a lathe headstock then feed the hone tool straight into it from the tail stock. This is how gun barrel blanks are drilled; the hole stays in the middle of the spinning thing in the lathe headstock. A close second is to thread the full length die half way into a 2" long 7/8-14 nut then thread a "guide" die in from the other end; they meet midpoint in that nut. Then feed the honing tool through the end of the guide die into the sizing die so it stays very straight and well aligned with the sizing die neck. The way the link above showed the guy pushing the hone into the top of the die is guaranteed to make the die neck crooked or belled at each end if the die and honing tool are changed in their angular/circular orientation. Nothing keeps both hone and die axes in line.

Use a hole micrometer to measure how much the sizing die's neck opens up. Pin gauges are ok until it goes in easy; how much larger is the die neck that the easy-fitting pin gauge?

The die's neck should be .002" smaller than a loaded round's neck diameter. When the fired case goes into the die neck, it's neck will be sized down to the die neck diameter. When the case is withdrawn, its neck springs back about .001" or so. Therefore, the "interference fit" (proper term for the mismatch of one diameter to another) will be about .001". Not the ".002" neck tension" such dimensions used are commonly termed; If you're good with a caliper, you can measure the difference between sized case mouth diameter and bullet diameter to get the exact interference fit at hand.

How hard or soft the case neck brass is will also cause a difference in how tight the bullet's gripped for a given interference fit. How tight is measured by the industry standard; the release force needed to push or pull the bullet out of the case neck; measured in pounds. A 10% spread in release force is normal. Military arsenal ammo has a 60 pound releases force spec for service ammo, 20 pound for match/sniper ammo. I've used as little as 3 pounds for single round loading and 10 to 15 pounds is good enough for Garand ammo shot rapid fire.

Forster hones their dies to customer specs for $12 per die plus shipping. Send them the diameter you want with a check for their die or honing out your Forster die. Or, get RCBS or Redding full length bushing dies with two or three bushings in .001" steps to cover different case neck wall thickness. As long as neck walls don't have more than a .001" spread, that good for half MOA groups at 1000 yards.

With case necks properly sized, I'm convinced you can seat bullets very straight with a ball peen hammer or any conventional seater. Don't need an expensive seating die. Besides, seating die bullet chambers vary quite a bit in their diameters; some .003" bigger than bullet diameter. Neck walls too thin are easily bent if the mouth is too small for the bullet diameter.

Once you've got die necks the right size, decap your fired cases then clean them before sizing. You won't need the expander (neck bender) ball in the die. Case life will be longer because you're work hardening the neck half as much. And your press will stay cleaner if decapping is done with a separate tool.
 
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What brand of cases r u using? Full-length resize, partial fl resize, or neck size? Necks trimmed, or not?

LC-13, FL sized for 0.002" shoulder bump, annealed, trimmed, etc.

When i neck turn the 223 , there is very little drag from the expander in my RCBS standard FL die.

Yes, with the necks turned to .0115, they just kissed the expander.

There are some misconceptions about honing die necks. . .

So are you saying that a FL die with neck bushing will produce adequate concentricity? I thought the floating bushing would simply follow whatever eccentricity was already present, and add a donut to boot.

I'm familiar with ID honing (like the Sunnen hone referenced here), and I expect to be able to maintain whatever hole orientation exists in my RCBS FL die while expanding it a couple thousandths. I was thinking that would be better than a bushing die.
 
Remove the seating stem from the seating die and fit it to the bullets that you are using. The tip of the bullet should not bottom out in the seating stem - the inside diameter of the seating stem should contact the surface of the bullet without the bullet tip touching the inside of the stem.
 
So are you saying that a FL die with neck bushing will produce adequate concentricity? I thought the floating bushing would simply follow whatever eccentricity was already present, and add a donut to boot.
You're correct in your comments. Yet Sierra Bullets uses Redding full bushing dies on all their unprepped cases shooting their best match bullets into 1/3 MOA in their 200 yard range. The thing is, you gotta use cases with fairly uniform neck wall thickness. There's .001" or more clearance from bushings to their die chamber, so, if neck wall is too variable, the hole in it where the bullet goes will be off center. If the neck wall on a 22 caliber case has a .002" spread, the mouth holding the bullet can have half that much off center position of the bullet. Insignificant, in my opinion.

If a standard full length sizing die's neck is honed out correctly, sized case necks will be a little better centered on case shoulders. If you shoot your stuff no worse than about 1/3 MOA, you may see a difference between ammo that's straight compared to stuff with bullets a thousandth or more off center. Which is why some benchrest afficinados send a fired case from their chamber to a custom die maker so its chamber will size such cases exactly .001" down from fired dimensions. I don't think it's critical to have exact size reduction all over the case. As long as it's a little smaller so the case body, shoulder and neck are well in line, a slight taper difference doesn't matter.

The case shoulder centers the round up front in the chamber shoulder. So perfect, a .243 Winchester cartridge that's perfectly straight will put its bullet dead center in a .308 Winchester chamber. Yes, the back end of the case at its pressure ring may be off center .001" from the extractor pushing it there, or the case head moves a bit from firing pin impact.. The bullet will be a fraction of that off center in the bore when it fires. No big deal at all.

Yes, those bushings stop sizing case necks about 1/32nd short of the shoulder. It works fine with standard chamber necks. Tight necked chambers may cause interference with that doughnut so standard dies sizing dies that size the whole neck all the way to the shoulder are better for them. Tight necks do nothing to center case necks anyway; the case neck never touches them until after the bullets left the case. Case life will be 10% longer, if that's a big deal for you.
 
Yet Sierra Bullets uses Redding full bushing dies on all their unprepped cases shooting their best match bullets into 1/3 MOA. . .

Bart, first I really appreciate your help with this.

Since I'm setup to turn case necks, I can create uniform neck thickness. Since I'm in a factory chamber and an extra 10% of case life isn't important, the bushing die may be a good step.

But I'm still not understanding why eccentricity jumped so much during seating. Prior to seating, I was achieving all the concentricity (in and outside of the neck) that I was hoping for! Whatever the problem is, it didn't show up until seating, and this with freshly annealed brass.
 
But I'm still not understanding why eccentricity jumped so much during seating.
The cause may be too much force needed to push the bullet into the case mouth.

After trimming cases then deburring the inside of the case mouth, if the edge at mouth diameter is too sharp, it'll scrape bullet jacket slivers off in tiny curls. That unbalances bullets and requires extra force which can bend case necks. I suggest you use an Easy Out screw extractor turned clockwise in the case mouth to smooth that sharp edge. Then run the case mouth on an off a bronze bore brush spinning in a drill. The end result is a smooth round edge for bullets to slide past without scraping.

What cartridge spinner tool are you using? The tip is often twice as far from the case front rest as the case neck point depending on the tool or gauge used. Some show twice the bullet runout than others for a given cartridge. None of them align cartridges for bullet runout the same way barrel chambers do for firing them. I'm not surprised.
 
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Bushing full length sizers are the easiest way to go, but since you are neck turning already having Forster hone the neck on the sizer is likely the best way. Figure out what it will take to clean the necks up completely and use that to figure out what to hone it to. Seat a bullet and get an outside measurement as Bart suggested. He has pretty much laid it out how to do it.

Did you check concentricity of the necks compared to the case body? Was that good before seating a bullet? Did you check it on the case body, shoulder and neck before seating?

I have to agree that hard seating is likely the problem if the cases were OK before that.
 
. Figure out what it will take to clean the necks up completely and use that to figure out what to hone it to
Subtract .002" from turned neck diameter with a bullet seated in it. That's the die neck diameter needed.

Not enough neck sizing if loaded neck and die neck are equal; sized neck will be bigger as it springs out a bit from die neck diameter
 
I'll add that I think the best way to use "neck tension" as a descriptor of how tight case necks grip bullets would be better served by using the difference in case mouth diameter from bullet diameter. Doesn't matter what diameter the case outside neck or die neck diameters are; bullets in use don't touch those areas.

If the bullet outside mic'd .2242" and the case mouth is inside mic'd .2234", that's .0008" of neck tension. In machine shop talk, it's that much interference fit.
 
Yes, and that is how I record it on loads I am trying to get top accuracy out of. I use a mic for the bullet and pin gauges for the neck ID. I have played with an inside mic but pin gauges have been more consistent for me, although I likely need to upgrade the mic. I cheaped out on the one I have. I knew better. Dang it. I also check the neck OD after seating a bullet. A holdover from loading for a tight necked chamber.

Then next is feel when seating, because even with painstaking care one or two here and there will feel different seating. Much easier to tell the ones that are different when using light neck tension.
 
The cause may be too much force needed to push the bullet into the case mouth. After trimming cases then deburring the inside of the case mouth, if the edge at mouth diameter is too sharp, it'll scrape bullet jacket slivers off in tiny curls.

Redding said the same thing when I asked them on the phone this afternoon. I'll have to study my chamfering; your suggestion of a EZ-Out is brilliant. I've been using a sharpened RCBS handheld. They also suggested seating in small steps to let the neck & bullet spring back in between.

What cartridge spinner tool are you using? The tip is often twice as far from the case front rest as the case neck point depending on the tool or gauge used. Some show twice the bullet runout than others for a given cartridge. None of them align cartridges for bullet runout the same way barrel chambers do for firing them.

I have a bit of a machine shop, so I built my own from a retired tailstock v-block guide bearing, and ground out portions so that it bears on the case just forward of the extractor groove, and just behind the shoulder. I know that's now how the cartridge centers in the chamber with the pin pushing, but I couldn't see a practical way to make a chamber-type shoulder-bearing concentricity gauge with materials on hand.

Did you check concentricity of the necks compared to the case body? Was that good before seating a bullet? Did you check it on the case body, shoulder and neck before seating?

Yup, inside and outside necks before seating, and necks and the front edge of the bullet's major diameter after seating.

Thanks gents! I have a couple leads to chase down.
 
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