Excessive runout

[stilllookin']

After getting encouraging measurements for banana bend (within .001 to .0025), I checked my freshly loaded cartridges for bullet run-out. It is so bad I can see the bullet wobble on the gauge (NECO Concentricity Gauge). I'm using the same RCBS press that has produced much better results in the past. I've got 40 loaded (will check the first few next time). Any suggestions for what might be going on?

 

[dahermit]

Not enough information. However, It is likely some problem originating with the dies...not your press.
What brand of dies. What changes since getting "good" run-out. Have you inspected and cleaned your dies? A bug could have crawled into your seating die and died. etc.

 

[TXGunNut]

Check the shell holder for cleaning media or other foreign objects. Could be why there's always a toothpick close to my press.

 

[snuffy]

I checked my freshly loaded cartridges for bullet run-out.

For what, handgun, rifle, shotgun? Specifically just how "BAD" was it?

 

[wncchester]

Most run-out comes from the case necks, no die or press can eliminate that.

Second most common cause of runout is excessive "bullet tension". Any bullet-to-neck diameter difference greater than 1.5 or 2 thou IS excessive. Overly tight necks only increases seating effort. That bends the necks as the bullet enters while doing absolutely nothing to increase bullet pull.

 

[MOREAMMO]

I had excessive runout when loading 9mm. The problem was with the dies. The seater plug was not contacting the ogive when seating, and was only seating off of the tip of the bullet. Changed to a hornady seater die and eliminated the issue. RCBS had sent me a new seater plug, but they sent me the same plug with the same issue. They offered me a "custom" seater plug if I sent them 5 bullets. So, long story short my issue was the seater plug in the die.

 

[woods]

It could be the brass. I have had brass that had a neck variance from .009" to .017" on the same neck. Do you have a ball micrometer so you can check neck brass thickness

Are you sizing with an expander ball? The expander ball could be offcenter and jerking the neck sideways. They usually do. I avoid expander balls like the plague.

Probably the brass though.

 

[stilllookin']

Excessive run-out

Thanks for the responses.

.270 Winchester is the cartridge. RCBS dies. Run-out is as high as .015 and more. I've put 7 loads through these Lapua cases, whose neck thickness I trimmed when they were new. I don't have a ball micrometer, but the NECO gauge should check for that which I will do, along with checking the shell holder and die. Nothing has changed with the die, which I keep in its original container. I will, however, take it apart for inspection.
Yes, I use an expander ball (which I will also check). What's the alternative?

I think that addresses all your (collective ) points. Let me know if I missed anything. I'll get back to you after I've checked for problems. Thanks again.

 

[Bruno2]

I was having run out problems with my rcbs dies in .223. There are so many factors that contribute to run out its hard to nail it down. I have multiple posts regarding the issue somewhere around here.

The other option from using a neck bender ball or expander ball as some call it it to use a bushing die. that resizes the neck with a bushing that squeezes the outside only of the neck.

I spent a ton of money on some Redding competition resizing and micrometer seating dies that fixed my problem .

RCBS will give you some good customer service . They will do whatever it takes to make you happy. I think having a custom seater made would be counter productive b\c then thats the only brand of bullet it would be good for.

 

[woods]

The best alternative to the expander ball is the Lee Collet Neck Sizer. It has a floating mandrel and collets that squeeze the neck brass onto the mandrel. Sizes very straight necks and you do not have to lube inside the neck.

However when your case gets tight in your chamber after 3 ro 4 firings you will need to push the shoulder back. For that Redding makes a Body Die that will size the case body and push the shoulder back without sizing the neck. You use the 2 in combination.

Another way to get rid of the expander is to use a bushing die. You buy a specific size bushing that will size the outside of the neck only. It will come with an expander assembly but most use the bushing die without it. They are expensive and you would get the best results if you outside neck turned to an even neck thickness so the thickness variations would not be pushed to the inside of the neck where they can bear on the bullet.

Lapua brass is very good brass. I did not know that Lapua made 270 brass, did you neck 30-06 brass down to 270?

 

[dahermit]

I had similar problems with bullet run-out with RCBS .257 Roberts dies. They produced loaded cartridges with a run-out of .017. I switched to another brand of dies(Forester I think), and that solved the problem. If it happened to me today, I would just get a Lee neck size die. All the Lee neck size dies I have used produced less than .001 run out.

 

[dardascastbullets]

Runout is also caused by the base of the case(s) not being true with the centerline of the case. This can be corrected by machining the bases true to the centerline. A Wilson Trimmer with the appropriate case holder will remedy this. Then reverse the shell holder and machine the base(s) until there is complete cleanup around the entire base. Now you can true up the necks. Your dies need to be perfect as well. Especially the seating die. There are some excellent benchrest seating dies currently being made as well as some of the 'old' seating dies.

One thing to keep in mind about the bases - they will not stay true if your bolt face is not square to the centerline of the chamber (or if there are high spots on the bolt face). And this is really where I would start - make sure that it is perfect.

Good luck with your shooting!

 

[Unclenick]

Hate to disagree, but I don't think you normally want to machine the case heads that way unless you first indicate the runout of the inside of the head to show it is square to case axis. Otherwise that trim will make the head thickness uneven from inside to out, which makes the case stretch unevenly in the chamber on firing. It then becomes what Merrill Martin calls "banana shaped". He demonstrated such cases are less accurate than axi-symmetric ones, as you might imagine.

Case heads gets re-squared to the bolt face every time you fire the gun. If they are ejecting from the gun out of square, you have a bolt face that isn't square, are getting uneven bolt lug contact, have an off-axis chamber, or some combination of all the above. These are all common problems. They call for bolt face truing, lug lapping, or rebarreling or setting back and rechambering the existing barrel, respectively. The last approach requires taking a careful truing cut that follows the case taper with a boring bar in the old chamber first. That is needed to prevent the reamer from deflecting off axis while cutting the new chamber. How much you have to set the barrel back then is just however deep you have to go so the back end isn't over spec; whatever it takes to let the reamer mark the new chamber contour all over is best.

We had one fellow at The Shooter's Forum who had a combination of these problems that were so severe he could only rechamber a fired case if he put it in with the same headstamp orientation every time. If he rotated it 180°, he couldn't chamber it without a slamming the bolt hard. Once he had fixed the three items I mentioned, all was well and the cases came out true.

 

[dahermit]

Run-out is also caused by the base of the case(s) not being true with the centerline of the case. This can be corrected by machining the bases true to the centerline.

When a cartridge is chambered, it lays in the bottom of the chamber. When it is fired, the case expands and fills the chamber leaving the head of the case where it was...at the bottom. All fired cases will show an off-set head. When you resize a case, it should not resize the head that is off center. When a person uses a egocentricity gage, the cartridge is supported on the body of the case, not the head. Therefore, the head being off-set slightly has nothing to do with eccentricity of the bullet.

 

[Unclenick]

In bolt guns and most self-loaders, the ejector is usually pushing the cartridge forward. If there is not enough headspace for the ejector to push the case rim against the extractor hook (in which case the cartridge will be biased toward the ejection port side) that forward thrust will tend to center at least the shoulder of the case in the chamber. The back end lying on the bottom of the chamber may have some effect on head offset, but I think if you use the inside case anvil on a Neco gauge to measure runout of the case wall back near the head and mark the high spots, you'll find the case expands first where the wall is thinnest, so that side stretches most to meet the chamber wall, and that's what causes the lateral offset.

If you don't have the gauge, you can test this for yourself by firing all your cartridges with the headstamps inserted upright in the chamber. If the offset doesn't always tend toward the bottom side of the headstamp, but rather is randomly scattered around the headstamp orientation, then you'll know it was wall thickness variation that is the culprit. I find wall thickness TIR near the head is usually about twice what it is at the neck, so it can be quite different.

 

[zeke]

Couple suggestions, just to try.

Use a once fired case to align the sizing die. This is done by not tightening lock nut, untill case is fully in die. Leave the expanding plug slightly loose, so it doesn't pull the neck out of alignment. Or don't tighten the locking nut on the expanding plug untill it is already started in neck.

Outside of buying a comp seating die, you could try a lyman case neck expander die for the next smaller caliber. This may enable ya to start a flatbase bullet in case straighter, before seating it.

 

[wncchester]

"When it is fired, the case expands and fills the chamber leaving the head of the case where it was...at the bottom."

I can't prove it but I don't believe that's true. More likely the case will give way at the weakest point in the wall just above the web and expand there no matter how the case may have been laying.