What level of runout on brass would you accept after using FL sizing die?

[Mr_Happyface]

I was never blessed with the ability to type succinct thread titles.


Alright, I have a full length sizing die with interchangeable neck bushings, (not going to name the brand but very high end, used on a co-ax press) and after resizing I'll put the brass on a concentricity gauge with the indicator halfway down the neck it shows 0.004 runout.

I've tried adjusting and setting up the die every way possible, left play in individual areas and measured the results of each, and I was able to get it down from 0.007 to the above, but this is the best I can do after a few hrs of work.


New brass straight from the box is showing LESS THAN 0.001 believe it or not.

This die does have an expander, and removing the expander does nothing to improve concentricity, leading me to believe this is not an issue involving neck thickness uniformity (although next test is to turn necks and note result).

What amount of runout on brass can you live with?


EDIT: Tried neck turning, no effect.

 

[bigedp51]

Size the brass in a non-bushing full length resizing die without the ball expander and measure runout. Then size again with the ball expander installed and remeasure for runout.

If your brass does not have uniform case walls and neck thickness the case will warp when fired because the thin side of the case will expand more than the thick side when fired. This leaves you with a warped banana shaped case with excess runout.

Any time you have less runout on new brass and fired brass has more runout you have bad brass or possibly an out of round chamber.

I have neck bushing dies and I have better luck by using a standard full length die with the ball expander removed sizing the case, then use an expander die on the necks and get less runout.

You can't make a silk purse out of a sows ear and you can't make bad brass better by sizing it when the case is not uniform in thickness. I have a case neck gauge and a runout gauge sitting side by side on my bench to compare fired and sized brass. If you have unequal neck thickness you will also have unequal case wall thickness and excess runout.

Below, even after neck turning with bad brass the case will still be off center with the bore and have excess runout.

This is why you will always get better accuracy by full length resizing, this removes the body and neck of the case from causing alignment errors by not touching the chamber walls. The bullet will be supported and aligned by the throat with only the base of the case being supported by the bolt face.

 

[eicas]

bigedp51,

Thanks for the insightful response on this. Answered questions for this newb too. Could you expand (pardon the pun) on HOW you go about the second sizing WITH the expander ball? Just run it through? Have you polished the expander at all?

Thanks

 

[918v]

When you fireform a case in your chamber it expands. This expansion stresses the brass. When you resize the case you stress the brass some more. When you stress metal it warps. Hence the runout. You can have the best quality dies but they can't stop the case from doing what it wants to do.

After going down that road and suffering disappointment I ended up with a Redding body die and a Lee collet neck die. I anneal after every shot and my runout is within .003"

Also, understand that brass tends to expand in the direction of empty space. A round in your chamber is being pushed against one side by the extractor. So it tends to expand in the direction of the extractor. When you resize the case, the die does not restore the base to the original factory dimension. So the case shows a bulge on one side. And there's the problem: the sizer sizes the case so the neck is in line with the case head. But the neck is no longer in line with the center of the body because the base is bulged more on one side than the other. Then when you spin it on your gauge, and that gauge indexes off the case body, you'll show runout.

After several loadings, that bulge evens out and assumes an even profile all the way around the base. Magically, runout disappears. It takes about five reloads to accomplish this.

 

[Mr_Happyface]

Interesting, thanks for the help. I should add that none of these rounds have been fired yet. The barrel is still at GA getting chambered.

This is a semi-wildcat caliber (7LRM), so my die options are limited. I had this die set custom made because I wanted the option to use neck bushings, but I might buy the el-cheapo Hornady FL die they offer and give it a shot anyway.

I was starting to suspect that this was due to case body thickness variation, this brass is unfired, so the springback when FL sizing should be uneven if the body is uneven, right? Neck turning kind of narrowed it down to the die or the case body.

Unfortunately I'm limited to one option for brass: Hornady.

How much should I bump the shoulders back to make up for this runout? .002?
I still haven't tried seating a bullet, but I'd imagine it's not going to improve on the amount I'm seeing in the brass to begin with.

 

[flashhole]

I recently did a batch of fifty 25-06 that I re-form from HXP headstamp 30-06 brass. I just use a Lyman FL sizer die with the expander button in the die to do the re-form.

After the initial re-size I sort by runout. Always the runout matched the non-uniform neck wall thickness. About 1/3 of the batch measured .004" variation in neck thickness.


I turn the necks (inside ream and outside turn) using the K&M tool. Then load them up and fire-form them in my gun.

The next sizing is neck size only using a Lee Collet Neck Die. Runout is very low, typically less than .001". Most don't even make the needle move on the gage.

If i were really concerned about squeezing out the best accuracy I would measure and sort the brass for uniformity before I did any re-form and use only the best brass.

You might have better results after the first firing if you already turned the necks.

 

[bigedp51]

One of the main causes of neck runout is caused by the expander button being locked down off center and inducing neck runout. This is followed by non-uniform brass warping when fired and inducing neck runout when the case becomes distorted after firing.

Complete Precision Case Prep within AccurateShooter.com

Expander Mandrels and Neck Tension within AccurateShooter.com

The Rifleman's Journal: Reloading: A Few Concentricity Questions

The Rifleman's Journal: Reloading: Partial Neck Sizing

 

[Mr_Happyface]

One of the main causes of neck runout is caused by the expander button being locked down off center and inducing neck runout. This is followed by non-uniform brass warping when fired and inducing neck runout when the case becomes distorted after firing.

Rgr, the expander is floating via o-ring.

I removed it entirely, but I noticed no change in runout either way. I'm just going to leave it removed so I have better control over neck tension.

The cases are unfired, so the ejector is not an issue.
This really leaves nothing aside from case body inconsistencies causing uneven springback after sizing. It's a high-dollar die vs. Hornady brass. I'm guessing the brass is the issue.

 

[No1]

run the first case into the die and tighten the lock ring with it in place. I've done this for a long time and that is the one step I will not skip, give the most consistent results whether FL or FL bushing or NK or bushing NK sizing.
You will also never correct an already sized case. Size it, load it, shoot it, then you can resize it again.
Do leave the expander out if you are bushing sizing.
To answer your original question, .0000"-.0009" is acceptable to me at this stage in the process.

 

[Mad_Charlie]

I also use Hornady Match brass and the floating expander technique, my runout is usually .002-.003.

I normally can cover a 7 shot group with a dime at 100m, from a bone stock except for trigger, SPS-Tac.

Maybe reaming instead of turning? guessing here...

 

[flashhole]

I use No1's die alignment technique too. Run the case into the die before you lock the die down. It works really well.

 

[Fatelvis]

One of the main causes of neck runout is caused by the expander button being locked down off center and inducing neck runout.

Would using Redding's floating carbide expander ball eliminate the off center problem? I started using them on all my bushing dies thinking that it would help with runout. Tell me I didn't waste my money!! Lol

 

[bigedp51]

Mr_Happyface

Your brass had "LESS" runout before you sized your cases, think about it, and now it has more

You also have a bushing die and the bushing "floats" and can move up and down, side to side "and" also "tilt".

A standard non-bushing full length die will straighten the exterior dimensions of the case more so than your floating bushing die. With a normal non-bushing full length die and the expander ball removed after sizing you should have the "least" amount of case neck runout. After this you troubleshoot the expander ball and seating operation for increased runout.

When I think of a bushing dies I think of brass that has already been inspected and sorted for neck uniformity and then neck turned. Meaning sizing a already prepped and straight case that has little to no runout.

From what you have told us for some reason your dies are inducing runout to your new "unfired" cases and this needs to be sorted out.