Concentricity issues. UPDATE

[amlevin]

I've had an issue arise lately. Concentricity of finished rounds.

I check indicated runout of the case necks after firing and they're as straight as can be expected. I then size using my Forster Shoulder bump/neck size bushing die. Neck runout increases to as much as .004". This occurs with the bushing 1/8 turn loose as Forster recommends as well as tight.

This run-out carry's through to seated bullets as well. Ranges from .0015 to as I said, .004".

I have even indexed the bushing and rotated it 180 degrees in the die body to see if it made any difference.


This occurs on 1X fired brass as well as 5-6X fired. Lapua, Winchester, BHA Match, and Federal. Annealed or not. Frustrating as it all comes out of the chamber nice and straight.

Any ideas or suggestions? Any known issues with this type of die?

BTW, the seating die is a Forster BR Seater Die and whatever runout is measured at the neck is exactly the same on the seated bullet. The Seating die doesn't change anything so I'm of the opinion it's not the problem.

 

[lawrence97]

Re: Concentricity issues.

Maybe try cleaning out your sizing die to get old lube and gunk out to see if it makes a difference. I usually spray carb cleaner to clean/flush it out.

You can also try an o-ring under the lock ring so that it can self center on the cartridge.

 

[BaconFat]

Re: Concentricity issues.

How many thousandths at a time are you reducing the neck size? You shouldn't reduce more than .005" at a time.

Another thought is that if you have been using the same bushings for a long time with no problems until recently,
maybe the bushing is worn out of spec. No more expensive than the Forster bushings are you could replace them
and see if that fixes your problem.

I had the same problem except they were with fairly new bushings. I measured the concentricity of each case before
and after each step of resizing. The culprit turned out to be the bore of one of the bushings was off-center by .001" or so.

 

[338 Mollett]

Re: Concentricity issues.

I have two Redding dies that do the same thing during sizing.The chamber is straight,fired brass comes out with no more than .0005 run out anywhere on the case you want to measure it.After sizing I checked the run out on the body first,.0005 great I thought then I checked the neck,up to .003 .004 run out.Like you I rotated the case to get it out but no luck,even bought 3 more bushings thinking they were the problem not so.The brass is neck turned accurate to .0002 that shouldn't translate to .004 run out.I called them,the response was that .002 or .003 is with in spec.I replied you are gonna have a hard time convincing a competitive shooter of that.There is no telling how much run out will be on the seated bullet.

 

[amlevin]

Re: Concentricity issues. Part Deux

I decided to go back to my F/L forster die to see if I could actually size a case and get nominal run-out readings. Using the same shellholder, press, and cases, I measured no more than .001" runout on 50 cases sized with my Forster BR F/L sizing die. Most were closer to .0005" which is more like it.

This ammo is going into a new Barrel I recently had installed by Benchmark and there is very little difference in body dimensions from Fired to F/L sized. A nice tight chamber. Only downside is that I have to expand the case necks so for now I'll just F/L size without the expander ball and expand using a Sinclair Expander Die. I anneal frequently so I don't expect any case splitting issues to crop up.

I may just send the die and questionable bushing back to Forster and let them pull their hair out.

Maybe try cleaning out your sizing die to get old lube and gunk out to see if it makes a difference.

First thing I did. I'm one of those guys that buys Brake-Kleen by the case. I hate "Gunk" and "old lube" with a passion. Dies get "hosed out" and cleaned with a Q-Tip after each session then wiped with a Q-Tip smeared with some Hornady Unique before put away. I find that when one puts away a dirty tool they tend to just pick it up and use it again, and again, until it's so filthy it causes problems.

 

[338 Mollett]

Re: Concentricity issues.

Glad that old die worked out for you ,I'm still scratching my head on my results.Maybe we put too much into this but I feel this is one of the variables we should be able to control a little at least for peace of mind.

 

[amlevin]

Today I was working off my "Turkey Coma" from yesterday and decided to check the uniformity of the bushing for this Forster Shoulder Bump/Neck Size Bushing die. In short, it wasn't.

I first checked the thickness using my RCBS Case Master Gauge. Ran it in one of he V-Blocks and found that it had a goo .001" of runout at one end, guess where? Right where Forster stamped their name and the size of the bushing. Their "Name" had deformed the surface more than just the three numbers.

Using a diamond lap and an Arkansas stone I worked these areas down to meet the main body surface. Checked runout in the same manner as before and read less than .0003".

I then took a couple of cases and measured the runout just as they came from the chamber after being fired. All read ~.0005" - .001". I then sized them and in every case they all measured <.001" with a couple down as low as .0003" TIR.

This equals the results I got with the Forster F/L BR Die. All sizing was done with the bushing firmly secured by the retaining "nut", not 1/8" loose as Forster recommended

In summary, it appears that Forster is stamping or rolling their Name and Size markings into the bushings which is upsetting enough metal to hold the bushing off-center in the die body. Perhaps they should consider either "electro-etch" or "Laser" to apply their markings.

Glad to be able to go back to the Shoulder/Neck bushing and not have to size the rest of the case. I'll enjoy the extra powder capacity albeit very slight due to the tight chamber 8)

Thought I'd share as there were a couple others who had a similar problem.

 

[BaconFat]

.... In summary, it appears that Forster is stamping or rolling their Name and Size markings into the bushings which is upsetting enough metal to hold the bushing off-center in the die body. Perhaps they should consider either "electro-etch" or "Laser" to apply their markings.

This is interesting that you suggest Forster change to a non-impact method of marking the bushings. I'm wondering if maybe they already have. I have a .341 and a .339 bushing that are marked in such a fashion. I was thinking that maybe these two bushings came from another factory who just did things differently, but I don't really know.

 

[amlevin]

.... In summary, it appears that Forster is stamping or rolling their Name and Size markings into the bushings which is upsetting enough metal to hold the bushing off-center in the die body. Perhaps they should consider either "electro-etch" or "Laser" to apply their markings.

This is interesting that you suggest Forster change to a non-impact method of marking the bushings. I'm wondering if maybe they already have. I have a .341 and a .339 bushing that are marked in such a fashion. I was thinking that maybe these two bushings came from another factory who just did things differently, but I don't really know.

If they haven't they certainly ought to consider doing so. I have 8 bushings in total from Forster and they're ALL marked with "stamped" or "rolled" markings. Some are a lot more pronounced than others and the external runout is attrocious on those. I'd vote for "Laser Etching" as it is even less likely to leave any raised material than electro etching.

I intend to share my findings with Forster. Who knows maybe I can exchange the rest of my bushings without having to hand work them for proper performance

 

[stool]

its not new. i mention it in another thread.

 

[Dolomite]

Sorry to bring up a old post but what was the result? Did forster mention anything? did you sand the etched wordings down some to make the bushing more concentric on the outside?

Please let us know...

 

[PigButtons]

hold your cursor over the name of the poster on the left, you'll see that amlevin hasn't been seen since 2018. He's not likely going to reply. just trying to be helpful.

But I did like seeing this thread as I wasn't that active back in 2013 when it originally ran.

 

[Uncle Ed]

If you resize a case with a standard full length die and remove the expander the resized case will be as concentric as it ever will be. This is because the case body and neck are held in alignment with each other when resized.

With a neck sizing die the case body is not tightly held and aligned with the case neck. Meaning the body of the case can move slightly inside the die and not be centered with the neck.

With the Forster, bushing bump die you also have a bushing that can move from side to side and even tilt when sizing the neck.

At the Whidden custom die website they tell you on average they get more concentric cases with non-bushing full length dies.

As an example I get the least neck runout with a Forster full length die using the dies expander in standard SAAMI factory chambers. And I get the most neck runout with a Forster bushing bump die followed by any standard neck sizing die.

Bushing dies work best with custom tight neck chambers with neck turned brass. The reason for this is in a standard SAAMI chamber is the more the neck must be reduced in diameter the greater the chance the bushing will induce neck runout. Remember the bushing floats inside the die and can move.

There is a reason why so many reloaders use the Lee collet neck sizing dies. And this is because this die produces less neck runout than a bushing die in standard SAAMI chambers.

I also lapped the Forster bushing to remove the raised stamped numbers and it made no difference in runout.

Below the Redding bushing die FAQ has a lot of information. But the quality of the brass and how much the neck must be reduced in diameter effects neck runout with a bushing die. This same FAQ tells you if the neck thickness varies .002 or more to reduce the neck diameter a few thousandths more and then use the dies expander.

Tech Line & Tips (FAQs)​

Tech Line & Tips (FAQs) - Redding Reloading Equipment: reloading equipment for rifles, handguns, pistols, revolvers and SAECO bullet casting equipment (redding-reloading.com)

Tech Line & Tips (FAQs)​

https://www.redding-reloading.com/tech-line-a-tips-faqs/146-concentricity-problems

Concentricity Problems​

a.k.a Neck Runout With Bottleneck Cases

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.

In the photo below are just a few of the .223 dies I tested and the Forster full length non-bushing die produced the least case neck runout. The Lee collet die in conjunction with a Redding body die also worked very well. But I prefer only sizing the case once vs twice with the Lee collet die if full length resizing.

 

[Dolomite]

Thanks for the detailed explanation!!!!

 

[Dusty Stevens]

If you save money it will always cost you in the end. Buy good dies once- you get what you pay for i assure you. But this is a good post on where runout usually pops up (hint: its rarely the seating die although thats where people concentrate their efforts)