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Discussion Starter · #1 ·
My wife bought me a Sinclair concentricity guage for Christmas. It shows that my cartridges average about .004" of runout regardless of the sizing die I use in the press. The press is a RCBS rockchucker and I use Redding S type neck and full length dies. Is there a way to reduce or eliminate runout without buying a new press?

I've measured the runout on my case necks before sizing and the variance is less than .001".
 

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The Troll Whisperer (Moderator)
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Try seating the bullets in increments, turning the case a quarter of a turn each time,
 

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kdub beat me to it. Seat a bullet part way, lower the ram and rotate the case, then fully seat the bullet.

The cause might well be a cocked seating die. That can happen because there is usually a gap between the die and the shellholder when we adjust the die. Coupled with the coarse threads of the press/die, that can lead to mis-alignment.

Correct it as follows: Loosen and back off the die lock ring without unscrewing the die. Place a flat, parallel piece of metal or glass between the die and the shellholder. Press upwards on the ram, holding pressure on the die. (That aligns the die in the press.) While holding tension, run down the lock ring until snug and lock it.

You can check the alignment in the future by placing that same flat object atop the shellholder and raising the ram until it barely touches the die. Look carefully and see if there is full contact between the object and die bottom. A wedge of air/light shows misalignment. A small piece of window glass works well for this because it has true parallel surfaces.
 

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While, IMHO, the Forster Co-ax press is going to give you straight ammunition more easily than other presses with a wider variety of dies, I've managed to get pretty straight ammunition even off an old Lyman Spartan Turret press with the right dies. If you are careful enough, you might end up having trouble seeing any improvement over the Rock Chucker, provided it was made with good alignment and symmetrically cut die threads. Ditto the die itself. Rocky's alignment check can help with that.

Concentricity involves four things:
  1. case neck concentricity with the case body
  2. neck wall thickness uniformity
  3. bullet seating straightness
I would have added a straight case body, but fireforming usually takes care of most of that. You do get the occasional banana shaped case that won't straighten under pressure, and it won't read a concentric neck no matter what you do. Set the indicator between the two case supports to see that. If the annealed case doesn't shoot itself straight, then you may simply want to set those aside for plinking, load development for pressure signs, firelapping, and etcetera.

If the case neck is not concentric coming out of the sizing die, it is being pulled by lateral force. A bullet seated straight into a tilted neck will still give you cartridge runout and the bullet will not be launched straight into the bore, which is the object of the concentricity exercise. An English shooter posted recently that an article in one of their magazines had tested all available sizing dies (though this probably preceded the new Redding sliding sleeve bushing neck die design). In particular, neck sizing dies are problematic since they don't grip the sides of the case while the neck is pushed and pulled through the sizing portion of the die, so there is a lot of leverage available for pulling the neck off-axis from the base end. A second opportunity to pull the neck off axis occurs when the neck is pulled over an expander. That's even a problem for full length dies, as the case body is unsupported by the sides of the die as it is withdrawn over the expander.

The only neck sizing die they found that applied no lateral force and gave resized necks that were consistently 0.001" or better, believe it or not, was the inexpensive Lee collet die. It flat out did better than any other die. It sizes the neck by squeezing it against a mandrel. That means no expander is needed. Moreover, that mandrel prevents the formation of "the dreaded donut" on the inside of the neck and shoulder junction, so you don't have to worry about inside neck reaming cases with a long history. Despite its modest cost, it seems to be a better mouse trap in principle. The Lee die takes a little getting used to. You may find you have to anneal case necks more frequently so it gives you its best neck tension. Every three rounds is good for consistent neck tension, anyway.

Neck wall thickness matters because the conventional neck sizing dies act on the outside of the neck, tending to make the outside concentric with the case body rather than the hole, though the Lee die creates a helpful compromise in this regard. If the outside is concentric, but not the inside, then even with the hole in the neck being parallel to the case body axis and with the bullet straight in that hole, you will still have runout. Sorting your cases by neck wall runout will eliminate that component of the runout problem. So will outside neck turning if you don't mind the extra working of the brass between firing and sizing that brings about? Again, frequent annealing addresses that problem.

Finally, you've got to seat the bullet straight. With conventional dies, sometimes interrupting the seating stroke with case rotating helps, as Kdub described. Other times it doesn't. That seems to depend on how straight the neck is on the case to begin with? The Precision Shooting Reloading Guide describes using an O-ring between the press and die nut to allow the die position to flex to self-align. A fellow who tried that on this board didn't seem to get any help from it. You could try turning the seater die into position loose (no nut) and use a mark from a Sharpie to locate its vertical position on the press, then just let it float in the thread to see if that helps? Just be sure the mark is lined up as you start each bullet in.

In my experience, straight seating is one place where the right die makes a big difference. The way I got straight seating on the Lyman turret press was to use the Redding Competition Seater Die. I understand the less expensive Forster version (apparently Forster came up with the idea, originally) works as well, but I don't own one to say for sure? When I first got one of the Redding dies, I found it put a bullet into a true .30-06 case straight enough that the runout was typically half a thousandth plus the neck wall thickness variation. That is with Sierra match bullets, so YMMV with others, but it is a good starting place.

Both the Redding and Forster use sliding sleeves that line the case up, and a floating seater plunger that lines itself up with the bullet tip. I understand second hand that other brands of sliding sleeve seaters have not proven to be up to the Redding and Forster products. Apparently they are the only ones on the market that have the necessary machining precision and to have achieved the necessary full case alignment. The Forster is available with or without micrometer adjustment, so a less expensive version is available to try. The Redding is micrometer only. I like the convenience of the micrometers, but they are a luxury and not a necessity.

Finally, you can bend a crooked bullet into place. NECO makes a special all-bullet fixture for this, but you can just drill a bullet-size hole in a piece of wood. Stick the bullet end of a cartridge in and by trial and error put enough lateral force on the case to straighten it. I have no idea what, if anything, this does to neck tension. It's a lot of extra work if you can avoid it, but it should give you a chance to see how much difference concentricity makes in your rifle before investing in the different dies.
 

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Discussion Starter · #5 ·
I've been drooling over the Forster coaxial press for some time now. I won't be able to afford it for a couple of months so I'll try some of your suggestions, including buying the Redding competition sizer. I am using the Redding competition bullet seater which aligns the case with the seating stem so I suspect that problem occurs during neck sizing. I've measured the runout of a pre-sized fired case and the concentricity varies less than .001". Once neck sized the neck appear to be about .003" out of alignment. Thanks for all of your suggestions.
 

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Discussion Starter · #6 ·
I just tried the rotation technique while sizing and seating. Runout improved by about 50%. Runout now is about .002". I'll keep working on it.
 

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Get a Lee Collet Neck die for neck sizing. Take the bushing and expander button out of your S die and use it like a "Body" die to FL size the case. Now you will have very concentric brass, couple this with a Forster BR seating die and you are all set.
 

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Eric,

Let us know how the competition sizer does? As I said, I don't believe it was out when that review was done, and I'd like to hear how the brass does with it by comparison to what you've been getting? But don't let the low price of the Lee collet die put you off it as a possibility, either. It is just works on a mechanical principle that makes it easier to maintain alignment.

Also, when I first got the Competition Seating Die, I was F.L. sizing military brass, and not getting any significant neck axis pull-off (I use one of the carbide sizing balls, and those seem to let the case pull off without adding much lateral pressure). I did not, however, consistently get below 0.002" at first, and that proved to be entirely due to neck wall thickness variance. So, don't expect to do much better than you are until you know you are measuring runout with a case that has a uniform neck wall. You should, if all goes well, be able to eliminate the extra work of bullet turning with the new sizer, even with necks that are not uniform.
 

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Start with sizing, the case is centered in the shell holder by the die, I do not complain, there is .010 slack between the case head and the deck of the shell holder, I use the slack in the RCBS shell holder to size cases for short chambers, some Lee shell holders have .014 thousands slack, the slack allows the case to float when being sized, then when moving to bullet seating we use the same shell holder, problem, the seater die does not offer case support therefore the case does not (may not) center, so I have said a perfect seating die would offer case support for centering.

There are OLD shell holders that are better by design for centering , but it is not possible to use one for sizing cases for short chambers, and there are a couple of good/bad features.

To center the case by eliminating the slack it is possible to use a feeler gage between the deck of the shell holder and head of the case to reduce the slack when seating, not as a technique or method but to determine if removing the slack will reduce case run out. RCBS has Gold Medal Match seater dies and Competition Rifle Dies, $65.00 to $85.00 for the seater die only.

F. Guffey
 

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Cv73,

I Remember an outfit had a gauge with bullet offsetting adjustment at Camp Perry years ago, then it disappeared off the market. The Hornady looks better as it appears you can set the gauge over the case neck or the bullet to read the difference due to uneven neck thickness. Then you could adjust the bullet offset so the bullet itself is what runs true, and not just the outside of the neck? Is that how your's works?

I may have to make a project of modifying my old Forster gauge to let me do that? The hole in the board method works for a lot less money, but is definitely more time consuming, being trial and error.
 

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"Get a Lee Collet Neck die for neck sizing. Take the bushing and expander button out of your S die and use it like a "Body" die to FL size the case. Now you will have very concentric brass, couple this with a Forster BR seating die and you are all set."

Roger that!

No sizer or seater can correct for non-concentric necks but that combo will work as well as it's possible to do with anything you feed them.

I've never found seating part way and turning does a thing. Once a bullet starts into my case necks out of line my concentrictiy gauge says they pretty much stay that way. Appears the seater stems have much too sloppy a fit in the die throats to be effective at correcting any significant off axis alignment.

One thing to mention about "run-out"; there is TIR (Total Indicated Run-out), which includes the needle's full swing both ways, and real run-out which is half of the TIR.
 

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I normally take a light clean up pass on the outside of all my case necks but, when I resize the case, whether full length or neck size only, bullet run-out is .0001 or less and I believe this to be contributed to the fact that I set my dies up in the press to "float" and as such, it cannot cock the case neck off center and keeps it in near perfect alignment everytime....

A
 

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My wife bought me a Sinclair concentricity guage for Christmas. It shows that my cartridges average about .004" of runout regardless of the sizing die I use in the press. The press is a RCBS rockchucker and I use Redding S type neck and full length dies. Is there a way to reduce or eliminate runout without buying a new press?

I've measured the runout on my case necks before sizing and the variance is less than .001".
What a cool wife....she knows what a concentricity gauge is!:D
 

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Discussion Starter · #15 ·
Yeah, she's pretty cool however I have to admit that I placed the order for her........

She also know what an infrared lighting system is for a CED chronograph...
 

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" I set my dies up in the press to "float" and as such, it cannot cock the case neck off center and keeps it in near perfect alignment everytime...."

My goodness Mr. ASSASSIN! Don't you know that dies should be tightened hard in a press with a big wrench or at least large pliers? ALL the "really good reloaders" do it that way don't they? And press rams MUST be a nearly rigid fit in the body so they can force cases into dies straight, right? :) ;)

(Not!)
 

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" I set my dies up in the press to "float" and as such, it cannot cock the case neck off center and keeps it in near perfect alignment everytime...."

My goodness Mr. ASSASSIN! Don't you know that dies should be tightened hard in a press with a big wrench or at least large pliers? ALL the "really good reloaders" do it that way don't they? And press rams MUST be a nearly rigid fit in the body so they can force cases into dies straight, right? :) ;)

(Not!)
Well Sir, here is the difference that I have found when targeting a rifle at 600 yards:

....... When dies are are tightened in the press, according to most die manufacturers instructions, and the die is set to bottom out against the shell holder, 5-shot groups @ 600 yards average from 5 to 10 inches...

....... Now, when a sizing die is set to float in the press and you don't jam the die up against the shell holder, these same rifle shoot 5-shot groups that are now averaging 1 1/2 to 2 inches...

I am one that no matter how many or how few rounds I will be loading, I still hand weigh each and every powder charge - one at a time. I take my loading very seriously because I HATE TO MISS!!!

A
 

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Perhaps I didn't make my "tongue in cheek" humor comments clear enough?

Okay, I meant I fully agree with you! Been making basically the same statement for years, including the value of at least a little slack in the ram. Every time I do I get flack from a covey of gun magazine experts. I was just trying to get ahead of them for you! :)
 

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runout

A question that has not been asked yet.
My wife bought me a Sinclair concentricity guage for Christmas. It shows that my cartridges average about .004" of runout regardless of the sizing die I use in the press. The press is a RCBS rockchucker and I use Redding S type neck and full length dies. Is there a way to reduce or eliminate runout without buying a new press?
These cartridges with the runout.....how do they shoot? What kind of accuracy are you getting from them in the firearm(s) that you use them in most frequently?
Pete
 
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