Does the neck thickness get thinner as the brass is weared?

H

HopeToBe

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I have not really payed much attention to this, however I normally cut the neck to a thickness of .0083'' which gives me a total size of .260'' given the bullets I use.

For fun I measured them today, they have been trimmed (cut length) twice, and the loaded rounds where all .2595''. Using the ball micrometer I found the neck to now be at .0081''. OK, it is not much and all of the brass had a consistent thickness of this.

Ensuring that my micrometer was not wrong in some way I measured some brass turned yesterday and they were all .0083'' as they were supposed to.

So - does it matter? Is it normal? I assume this favours keeping the numbers of times the brass is used under control, and this number of reloads should be more or less uniform across the batch of brass in use?
 
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You may get some better answers about this but I had this happen one time. What I was doing was cutting the neck in one pass with the turner. I had done this before with no problem but this time, I cut them a little faster. I remembered later that I thought the turner had moved and readjusted it but what actually happened, was by turning faster I had a wavy neck (under a magnification it looked like I was trying to thread it) but it really wasn't noticeable by the human eye. When I measured, I was measuring the high spots but afte a firing or two, it all smoothed out with the high spots flowing into the low, thus creating a thinner neck than I thought I had turned.

I'm sure there is more than one way to creat this but that's how I managed it.

Hovis
 
Some among us believe the brass in our necks doesn't flow :); not me you understand :) I blieve I know that it do. :)
 
Non Issue

I have 30BR and 6PPC Cases that I have fired countless times, and when I seat a bullet and measure the diameter, they do not seem to change over the course of the cases life.......jackie
 
I've had PPC and BR cases wear thinner over time. For me it takes lots of firings.

Case necks can't thicken. You can shove shoulder brass up into the neck from sizing wrong (donuts) but it can't get thicker on it's own. :)

al
 
Fifty five rounds fired thru Sako .220 Russian formed to a .262 neck 6 PPC and the neck remains the same thickness.

At this point I used some 70 gr Nosler for pratice - experimentation and opened up the primer pockets in five more firings.

And I read on the internet that this brass is not good-Ha!

Glenn
 
Also C O U L D depend on how you are cleaning your case necks.
I had some one time go thin and found it was because of what and How I was cleaning the necks.
 
mikecr said:
Hovis supplied a good answer.
How EXACTLY are you measuring your neck thickness?
Click to expand...

I use a ball micrometer and measure the neck thickness at 3 different places. Micrometer has a 0.0001''.


Vern said:
Also C O U L D depend on how you are cleaning your case necks.
I had some one time go thin and found it was because of what and How I was cleaning the necks.
Click to expand...

Could you elaborate on how you did do it when the started to go thinner? Or the other way around.
 
When you say 3 different places, is that circumference, or distances from mouths?
Do you stop the mic at a standard depth, that is the same as earlier measurements?

Given that your cases are sized to the point of trimming requirement, your necks should be getting thicker with a taper to thinnest at re-chamfered mouths.
 
When saying 3 places I mean 3 random places at the same depth to ensure that the thickness is equal all way around. I measure at the same depth as I do when I first made them.
 
HopeToBe said:
I have not really payed much attention to this, however I normally cut the neck to a thickness of .0083'' which gives me a total size of .260'' given the bullets I use.

For fun I measured them today, they have been trimmed (cut length) twice, and the loaded rounds where all .2595''. Using the ball micrometer I found the neck to now be at .0081''. OK, it is not much and all of the brass had a consistent thickness of this.

Ensuring that my micrometer was not wrong in some way I measured some brass turned yesterday and they were all .0083'' as they were supposed to.

So - does it matter? Is it normal? I assume this favours keeping the numbers of times the brass is used under control, and this number of reloads should be more or less uniform across the batch of brass in use?
Click to expand...
Unless you have a precision boring setup and have turned AND bored the case necks, measuring wall thickness alone is not the best. Turn a neck, then size it and seat a bullet.

Measure the diameter over the neck with that seated bullet, and at that, measure in 3-4 places to get an average.

The neck brass simply as extruded has minute waves in it (peaks and valleys) and you may in one measurement measure a valley then next measurement you may measure a peak.
 
I believe in what jerry just had to say. I have spent literally hours on end measuring turned neck thicknesses and i came to the conclusion that the brass must not be perfect, or wavy as jerry has stated. It seems to be the only logical answer. Lee
 
Bottm line, it's 2tenths of a thou shift..
At this scale, he may need to accelerate necks through a Hadron Collider to measure the 'Dark Matter' within them..
I mean, ya know it's there!
 
I believe what jerry is saying to be correct also its being hammerd against the chamber causing it to flatten some what, Notice how the new cases grow after a few fireings ? Slam brass against steel what happens?
 
We know that the cases grow.
Where are they growing? is the body getting longer between base and shoulder?
Is the neck getting longer?
We trim them but the brass came from somewhere.
If the necks get longer then should we think the brass moving from shoulder to neck will magically stay the same exact thickness as the turned neck?
 
Vern said:
We know that the cases grow.
Where are they growing? is the body getting longer between base and shoulder?
Is the neck getting longer?
We trim them but the brass came from somewhere.
If the necks get longer then should we think the brass moving from shoulder to neck will magically stay the same exact thickness as the turned neck?
Click to expand...

The cases grow when the cartridge is fired.

The cycle is... the primer fires and forces the case forward in the chamber (with about 700 pounds of force), and leaves a bit of space between the bolt face and the case head.

Then the gases from the powder cause the case walls grab (and stick to) the chamber walls.

Then the case head is pushed back from the 3,500 to 6,000 pounds of force from the pressure in the case. The stretch comes from in front of the case head (the web).

So now, the case is longer by the amount that the case was pushed forward.

Then, when we load the case again, and when it is fired, the cycle starts over again.

Each time it is fired, the case is pushed forward, and the head is pushed back, so it grows slightly every time it is fired. Sharp shoulders help slow this cycle down, and wet chambers help by letting the case walls slide back (and not stretch), but when we FL size, or bump the shoulders, it increases the process (though it is necessary when chambering is difficult).

Bench rest shooters have to deal with this more than varmint shooters, because benchrest shooters need their cases to chamber easily so as to not upset the rifle, while a varmint shooter can deal with a "crush fit" case, which does not grow.

So, in summery, the brass that makes the case longer, does NOT come from the body, it comes from in front of the case head.
 
No, No
While cases can stretch on firing -due to excess headspace or low shoulder angles/high body taper, any significant body sizing contributes to brass movement thick toward thin.
A lot of FL sizing will lengthen brass, causing a need for trimming, even with no headspace.
This lengthening, is thicker brass being rolled up the case from near webs all the way to the mouths(eventually).

Op's necks should actually be a little thicker if anything, given that he's fired it to a point of retrimming.
One thing's for sure, his brass didn't go toward shoulders.
 
If with all that said it was accurate then,,,,,,, if and some do get 20 or more firings from a case and we continually trim that case to length then eventually we would have trimmed the neck all of the way down to the shoulder. And I have never seen that happen yet.
Also if it keeps stretching at the case head wouldnt there be a head separation after just a few firings?
 
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