Expander Mandrel Causing Neck Runout

[Zia Hunter]

Was processing some new RP brass in 220 Swift today. first step was to run the brass through an expander mandrel so I could neck turn with a Sinclair 4000. Took quite a bit of pressue to get the mandrel into the case neck (inside of necks were lubed). Decided to see if the mandrel was impacting runout and it fact it was. After neck turning, ran the brass through competition neck sizing die w/o the expander. Checked runout again and although better still out of tolerance (.004"-.006").

Any suggestions on how to correct? Will continue to finish loading and fire form the brass to see if that helps for subsequent loads.

 

[navyrad8r]

zia,
did you switch the expander mandrel for the turning arbor by accident? or do you have any build up on the turning arbor? give the turning arbor a spin through flitz, bore paste, or 0000 steel wool to smooth it out and remove any build up. is the expander centered in the die? throw an o-ring under your expander die to allow it to drift a little and find its own center? Just a few thoughts...i hope one of them helps.
holiday cheers,
doc

 

[Zia Hunter]

Doc:

Thanks for the reply. The expander mandrel was installed on a mandrel die in the press. The necks turned fine on turning mandrel mounted on the 4000. Need to expand the necks so they will fit on the turning mandrel.

Happy Holidays to you as well.

 

[bozo699]

Doc has some very good thought for you to try. Is the expander a Sinclair expanding mandrel or some other brand, it is important to use the same brand as they are matched up for each other. Also are you inside chamfering the necks, on some brass I find to keep runout to a min I expand with the turning mandrel first then the expander, after you fireform they should be concentric as long as your chamber is, leave your turner set and after fire forming if there is any variance in neck wall thickness you can re-turn, it will just take a skiff off and you should be good to go, hope this helps some.
Wayne.

 

[Zia Hunter]

Went back to shop after thinking about it. Took 5 new cases and checked all for runout and all were within .002. Ran 2 through the FL sizer with expander plug as recommened in other articles and checked runout. It increased significantly. Then ran 3 cases through expander mandrel and runout was not affected. So it appears the mandrel was not the problem but resizing was. Next time will run through a body die. BTW the madrels are Sinclair with cases trimmed to length and deburred and chamfered.

The rifle chamber is concentric and fire formed brass comes out fine although with a little longer headspace than new brass. Currently have the body die set up to bump fire formed cases .002" less. May readjust with shims so it will handle both new and fire formed cases or buy a second body die.

 

[bozo699]

Went back to shop after thinking about it. Took 5 new cases and checked all for runout and all were within .002. Ran 2 through the FL sizer with expander plug as recommened in other articles and checked runout. It increased significantly. Then ran 3 cases through expander mandrel and runout was not affected. So it appears the mandrel was not the problem but resizing was. Next time will run through a body die. BTW the madrels are Sinclair with cases trimmed to length and deburred and chamfered.

The rifle chamber is concentric and fire formed brass comes out fine although with a little longer headspace than new brass. Currently have the body die set up to bump fire formed cases .002" less. May readjust with shims so it will handle both new and fire formed cases or buy a second body die.

Zia,
the new cases are set back further then you need already so your body die you have setup for your fired cases won't touch the shoulders of your new brass but will size the body as needed, you won't need to buy another one, leave it set as is.
Wayne.

 

[Zia Hunter]

Bozo699:

Thanks for all the good information and will leave the body die alone.

 

[navyrad8r]

now pull the expander ball out of that die an save for something else. let your expander die do the work for you?
cheers,
doc

 

[BoydAllen]

Here's the deal. The ID of the neck portion of your one piece FL die is sizing the necks of your new brass down smaller than it is out of the box (bag?). The greater the amount of expanding the more friction, and pull on the case. When that pull gets too large, the case gives a little where the neck joins the shoulder. The problem is that it does not do so evenly. This cocks the neck as it is being expanded. It doesn't matter whether you are pulling an expander through, or pushing one in from the top. If there is too much difference between pre and post expansion diameters, the problem will occur. Since you are dealing with unfired brass, that is undoubtedly smaller than your chamber, there seems to be no reason to do anything but expand, turn, trim, chamfer and debur. As an aside, die expander balls have gotten an undeserved bad rap. If they are used in a die that does not size the neck down too much (more than a couple of thou. under expanded diameter) there is not problem with them causing crooked cases. The problem is not so much the expander ball but the dimension of the ID of the neck portion of the die. Another thing, you should set your shoulder bump relative to a tight case, and it takes two or three firings for them to get tight at the shoulder. I usually fire a case until its "headspace" no longer increases, sizing just enough of the end of the neck to hold a bullet, and save the case for a reference. All you are doing when you bump a case that is smaller, shoulder to head, than the chamber, is creating a bad fit.

 

[SAGERAT]

I'm using the 21st Century neck turner and its mandrels, working great. I use the Lee Collet dies for neck sizing, no runout problems with those, polish them down a bit for more neck tension if needed. For the decapping operation I just use a universal die, no expander ball. The expander ball is usually your biggest source of run out, case length growth, etc. Okay for the guy loading a box of 30/06 hunting ammo every 5 years, not okay for long range tack driving.

 

[Country]

I rekon the case necks are too hard and need annealing. Also clean and polish the inside of the necks with fine steel wool wrapped on an old bore brush and chucked in an electric screw driver.
Then square the necks up in a case trimmer and chamfer . Mix up some 50 % moly powder 50% fine graphite mix and apply well to the inside of the neck with quetip . The dry lube will not affect your powder load.

 

[fguffey]

“Took quite a bit of pressure to get the mandrel into the case neck (inside of necks were lubed)”

And there you are, I neck 280 Remington cases to 338 and 35 Whelen, when I expand a case neck the case is unsupported, some cases shorten .035 thousands in the process, most of the .035 is lost to neck shortening as when a neck is expanded it shortens, when sized down the neck gets longer, not because the neck gets thinner or thicker but because it gets shorter or longer.

If you want to determine the effect of necking up (or down) has on the case, measure before and after.

For a different reason, I have turned cases into bellows/accordions, there was/is nothing to be accomplished when measuring run out on these cases, the pressure created on the unsupported case body (column) could cause the case to split or collapse.

F. Guffey

 

[rocketron]

your neck runout my be a combo of pulled necks and a difference in neck thickness. a skim cut still leaves high and low spots.

how does a loaded round measure for runout?

fireform and check runout after each step.

 

[fdshuster]

country: " I rekon the case necks are too hard and need annealing". We're talking about new, never loaded RP brass, that has never been subjected to work hardening. I find it hard to believe that virgin brass would need annealing. Zia Hunter: I also get case neck runout anytime I run an expanding mandrel into a case neck. Just necked up a small number of new Lapua 6BR to 30 cal., using Lapua, and typical R/O's measure .004" to .006" on my Sinclair gauge. At this point I really don't care. They will straighten out with the first fire-forming. There may be an occassional one or two ( out of 20) that will always have some slight R/O for their entire life, compared to the others that will be less than .002", but I write those few off as having a slight defect since the time they were formed. If I feel accuracy may be compromised by these few, I keep them for first round foulers, basic scope adjustment & 100 yd. maximum distances, where I find it to not matter. Actually have gotten some very excellent 5 shot groups at 1 and even 200 yd. with R/O's as much as .004". Works for me.

 

[PREMOD70]

Welcome Swift user, after all the operations to the case I finish up with a Lee collect die.

 

[Shynloco]

Zia Hunter,
After reading all the comments, as well as having run across a similar problem with a different caliber (but the same out of wack runout in the end), I believe that fdshuster came up with the best solution I found noy lonmg ago with a few brand new unfired "more expensive" brass. And that was that simiply you've got some bad new casings where the necks were messed up during manufacturing and you simply might not be able to "rehabilitate" them no matter what you do. Save the ones you can and use them as fdshuster recommended. And what Boyd Allen said about the bad raps that expander balls sometimes get is also spot on. Bottom line is sometimes your basic product turns out to be junk and if you run them across a concentricity gauge as your first step, you'll be able to detect "issues" before you even to the usual first step in regular case prepping. Just my thoughts and what I've found first hand with the problem you described. Good luck and have fun.

 

[fguffey]

"Took quite a bit of pressue to get the mandrel into the case neck (inside of necks were lubed)"

It is as if the "quite a bit of pressure" is an isolated event and had/has no effect on the case. In the normal sequence of events when a reloader sizes the case there is no pressure applied to the neck when the ram is raised, the expander does not contact the neck, the expander contacks the neck when the ram is lowered, and no one knows what effect the expander has on the case/neck because they can not figure a way to measure before and after.

F. Guffey

 

[BoydAllen]

Figuring out what the cause is in the sequence you described is easy. Remove the expander assembly from the die and size a case, measuring it before and after, both as to diameters at various points, and for concentricity, comparing the latter with that of a case that was sized with the expander in place. Not brain surgery..

 

[fguffey]

“Figuring out what the cause is in the sequence you described is easy. Remove the expander assembly from the die and size a case, measuring it before and after, both as to diameters at various points, and for concentricity, comparing the latter with that of a case that was sized with the expander in place. Not brain surgery..”

No brainer, true, and no slide of hand, same case, neck down the case when sized, then neck the same case up. Then there is that part where the sizer ball pulls the neck, when it is pulled through the neck when the ram is lowered the neck gets longer? And that is the reason I say some of this stuff is made up and repeated over and over and over until some believe it to be true, and I agree, it is not brain surgery.

F. Guffey

 

[BoydAllen]

Cases get longer depending on how much the body is reduced in diameter , and the shoulder is bumped even when no expander is used. If the pull of a regular expander is high enough, the case may get longer because the shoulder yields. It is asymmetrical yielding at the shoulder that cocks necks when they are expanded, with an expander or mandrel.

Some time ago, I had forgotten to reset the bump of my 6PPC FL die, when I switched to a new, batch of cases. After a few firings and sizings, I noticed that I was having some accuracy issues, and, along with other things checked case lengths. They were quite a bit longer than I expected them to be, and when I checked the amount of shoulder bump, I knew why. They were getting bumped too much by the die setting that was for old, work hardened cases. Luckily it was a small batch. Because I knew that I would have probably thinned them, just above their heads, I tossed them, and made a mental note to be more careful in the future.

These days, I back off my die, when I put away my press, so that if I start my next range session with a different batch of brass, I will always have to reset the die.