Brass case wall thinner on one side than the other

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Brass case wall thinner on one side than the other

Post by disko » 03 Feb 2015, 12:22 pm

Hi guys,

I couldn't get a picture of this on the phone that was up to scratch so hopefully I can describe this well enough to get an answer.

For s**ts and giggles I cut open a .308 case just to have a look. The brass is 3 or 4 times fired.

I sawed the head off so I had just the tube. Looking down the tube, it's obvious one side of the case is thinner for it's whole length than the other. Looking at the base of the cut sort of looks a bit like a crescent if you know what I mean.

I know brass isn't made like this but if you imagine if you had a rod of brass and drilled a whole down the middle, but drilled the whole slightly off centre. Looks like that.

After that I cut the length of the case and folded it out like a little sheet. There was no separation beginning, just the thinner wall along one side.

Is that thinning from firing or a manufacturing discrepancy?
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Re: Brass case wall thinner on one side than the other

Post by Jack V » 03 Feb 2015, 3:04 pm

I would say it's from manufacturing . 3 to 4 shots is not much and they don't thin all along the length like that so much they thin in one spot around the circumference just up from the solid base . It's not uncommon with cheaper brass anyway . It's that thin side that would most likely give up first in a head separation situation.
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Re: Brass case wall thinner on one side than the other

Post by Tiiger » 04 Feb 2015, 3:14 pm

Jack V wrote:I would say it's from manufacturing.


Sounding like it.

How 'thin' is thin Disko?
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Re: Brass case wall thinner on one side than the other

Post by Techc » 04 Feb 2015, 3:20 pm

This got me curious.

Just to see I cut the base of a Remington case of to have a look and it was the same.

Marginally thinner on one side.
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Re: Brass case wall thinner on one side than the other

Post by disko » 11 Feb 2015, 8:11 am

Jack V wrote:they don't thin all along the length like that so much they thin in one spot around the circumference just up from the solid base


Yeah it's not head separation, just sounding like manufacturing tolerances.
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Re: Brass case wall thinner on one side than the other

Post by disko » 11 Feb 2015, 8:12 am

Tiiger wrote:How 'thin' is thin Disko?


Not paper thin.

I haven't got the calipers on it but it's thick enough. A hair under a mm?

Just thicker than neck thickness comparing to other cases and cut open another case to compared and it was similar.
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Re: Brass case wall thinner on one side than the other

Post by disko » 11 Feb 2015, 8:13 am

Techc wrote:This got me curious.

Just to see I cut the base of a Remington case of to have a look and it was the same.

Marginally thinner on one side.


Thanks for the confirmation :thumbsup:
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Re: Brass case wall thinner on one side than the other

Post by Gwion » 15 Feb 2015, 8:40 pm

This is just a theory i read else where in relation to reloading and seating depth:

When the bullet is not held by the lands of the bore, the case sits on the bottom of the chamber which acts as a heat sink. This bottom part remains thicker as the unsupported walls of the case expand. This could possibly happen in 3-4 firings depending on load and cartridge.

I read this in relation to fire forming cases with bullets seated to the lands in order to form the case with a more concentric neck.

Having noticed thicker and thinner areas on some Rem 223rem cases, i thought i'd experiement with this fireforming method.

Just passing on a possible cause, although it may well be just manufacturing tolerances as well. Would be good to compare new brass to 3-5 rounds of firings.

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Re: Brass case wall thinner on one side than the other

Post by Jack V » 16 Feb 2015, 6:54 am

Generally once the case is fired the first time after that there is less radial expansion taking place with subsequent shots.

A lot depends on how much sizing is done each time but if the sizing is done to achieve minimal headspace then no real excessive radial sizing will happen either .

A case can lay in the bottom of the chamber and does tend to expand up on one side to form that one sided ridge look . Not so much in match chambers because new brass fits tighter or may even need sizing slightly before it's ever fired , to go into the chamber . This way very little radial expansion ever happens just enough is allowed for reliable extraction .

I can't see that radial expansion would have a big bearing on case wall thickness that is observed over the full length of the case . That is not to say that some could not go on in the right circumstances but it's never been a recognised major issue as far as I am aware .

Cases are far more prone to length wise stretching having an effect on brass thinning around the circumference and possibly resulting in head separation which is very well recognised . The only way you would prove that theory is to start with perfectly even thickness brass and fire it many times and then cut the cases in half and re measure the brass thickness . It is quite common to section new brass and find some thickness variations from one side to the other . Usually if you measure the neck thickness all around on a new case any variations will also run all the way along the case and generally stop at the start of the solid head .
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Re: Brass case wall thinner on one side than the other

Post by Zilla » 16 Feb 2015, 8:06 pm

Maybe try and get your hands on a match quality case like Lapua or whoever.

Just to sate your curiosity, open her up and see how it compares brass built to a lower tolerance (supposedly).
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Re: Brass case wall thinner on one side than the other

Post by Swarm » 20 Feb 2015, 2:35 pm

I could mail you a match case if you like Disko.

PM me if you want.
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Re: Brass case wall thinner on one side than the other

Post by disko » 24 Feb 2015, 1:38 pm

Thanks mate. Done :)
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Re: Brass case wall thinner on one side than the other

Post by howtow » 01 Mar 2015, 6:54 pm

Gwion wrote:I read this in relation to fire forming cases with bullets seated to the lands in order to form the case with a more concentric neck.


"to the lands"

You mean actually touching, not the normal 5 or 10 thou off?
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