How to make a case concentric?

[AussieShooter]

Hi Guys,

I am having trouble trying to find information on how to make a case concentric.

Why the case you may ask,
It's simply because when trying to neck turn, the horizontal axis increases its radius at the shoulder and more so at the neck.

The fact is the further along the case you observe from the belt the larger the horizontal radi.

If I can fix the cases concentricity I can then neck turn so that the neck turning tools cutter is orthogonal to the neck for uniform cutting. This in turn will allow for the same neck thickness right the way around neck.

Any ideas?

 

[Shynloco]

From everything I've been encountered (over the years) and been told by various Die makers and shooters with years and years of practical experience in both amatuer and competitive shooting and reloading, if your brass has crooked bases, the only cure is to throw them in the trash as you simply cannot fix them. Now you might just want to use them as fowlers, but forget using them in competition as they'll start you out at a disadvantage from the get go. Just my thoughts.

 

[AussieShooter]

Thanks Shynloco,

I can see your method as a simple fix and use the brass that doesn't make the cut as test brass for annealing calibration.

My next question is how many thousands of an inch tolerance would be acceptable for precesion BR match brass?

 

[joat]

In my experience, neck turning when done with the tight fitting mandrel inside the neck, minimizes the effect of the rest of the case. Having the case locked into a turning case holder turned by a drill motor of some kind and the neck turner in the other hand you essentially have two turning centers separated by the human body. Hardly a machine setup. That is why it is essential to have a tight fitting neck mandrel with a proper depth set to turn into the case shoulder a bit and get concentric necks. You will see this when using a neck measuring tool as to how uniform the neck was turned. You turn a neck to get uniform neck thickness, not to true the case. If the neck is uniform and the case fired in a good chamber, the case will be concentric. Hope this helps.

 

[Hal]

Aussie shooter

Is your brass crooked or do the walls of the brass vary in thickness ?

 

[mysticplayer]

Fired it in your rifle and assuming your chamber is straight, the brass will be too.

Size properly and neck turn away.

Assume from your description you are trying to prep new out of the bag brass. If yes, then fireform and life is happy.

If this is fired brass, get another barrel and chamber it properly.

Jerry

 

[Lapua40X]

Perhaps I'm missing something here but, assuming we're using fired cases; if the case is "crooked" when it is ejected from the chamber the problem is much greater than the simple concentricity of the neck. The neck trimming tool takes its reference from the neck, relying on a properly sized mandrel, not the full length of the case. Therefore, theoretically, the only brass initially removed should be that surplus amount along the thickest wall of the case. Further trimming should then simply remove more brass with each turn (in equal amounts) until we've reached the wall thickness goal or (if we turn too far) eliminate the neck brass altogether.
If the head space is correct and the profile of the shoulder of the case matches the shoulder of the chamber the neck should center in the throat of the chamber.

 

[BoydAllen]

What caliber and what measurements are you dealing with? Also, what tooling have you been using to turn necks? What sort of tools are you using to measure cases. How much do your sizing dies reduce the diameter of your fired cases at the shoulder and about .3 above the head? Are you concerning yourself with the straightness of unfired brass?

 

[Shynloco]

Perhaps I'm missing something here but, assuming we're using fired cases;

To be clear, my comments were referencing NEW and UNFIRED BRASS that are found to be "crooked" (+.004 or more runout) from the get go. Have found it before even with top quality Brass and it's useless trying to straighten out a poorly manufactured piece of brass.

Alex

 

[AussieShooter]

I am using second hand brass.
Calibre is 308
I start off with the K&M expander opening up the mouth enough to use the K&M neck turning tool down to the shoulder.
Before using the neckturning tool I use the Wilson sinclairs trimmer with the Wilson adapter to make sure the mouth is trimmed evenly.
After evening up the mouth I use the Wilson case gauge with a mitutoyo micrometer to measure the case oal.
I then use the 21st Centuary to measure runout at the neck and different positions along the case.
I am getting a variance of upto .002.
I ideally wanted to know if this could be corrected for better brass uniformity.
I have a neco runout gauge to measure internal wall thickness.
I can't measure internal volume as from what I have read the best method is using water and I had preciously / received deprimed brass.

 

[AussieShooter]

Have ordered a neco runout gauge but I am awaiting on stock and postage.

 

[BoydAllen]

Got it. Now... this second hand brass, that you say is showing up to .002 runout, measured at the end of the neck, are you running it through a sizing die before you start the sequence that you wrote about? If you are, what sort of die, and how much expanding up are you having to do to get ready to turn? (difference in neck OD, before and after expanding)

 

[AussieShooter]

I have redding competion dies.
I tried putting a test case through the body die hoping that the walls would mould to the walls of the die but found it only pushed back the shoulder.
Doesn't help sinclairs didn't send me a copy of the instructions and I can't find them online.
I have dillon 550b that I plan to use and previously used for depriming, priming and powder throwing.
I found the plate has to much flex for my liking.

 

[bigedp51]

In the States we call a warped case "banana shaped" and since your trying to straighten or "bend" the case I have to ask.............

Are you from Queensland.

 

[AussieShooter]

Lol.
Nah, no banana bender here.
More inclined to a sandgroper.

 

[BoydAllen]

So, your cases are fired but not sized when you get them? If you measure the diameter of the cases, as received, at the shoulder, and about .3 up from the head, and take the same measurements after running them through your FL die, have they been reduced by sizing,and if so, by how much?

 

[amlevin]

My Dad had a saying that kind of covers this situation. If you start with crap, all you will get is crap with a new "finish".

Most of those I know who are anal over their brass either start with new or will take a huge batch of 2nd hand brass, inspect the cases for case wall uniformity, sort by weight, and only neck turn after fire formed in their rifle. Some will even repeat the process to make sure that when fire forming the case metal expanded uniformly. One shooter even sorts cases at this point by how much they expanded in length.

With some brass brands this may well be overkill, especially if it's a top end brand.

For those who are trying to save a few shekels on brass it's a way to build some batches of very uniform brass with only an investment of time.