How does brass "grow"

I'd like to understand the basics behind case expansion a bit better.

Assuming you have a cartridge that headspaces off the shoulder, and you are loading fire formed cases for a single rifle.

After each firing the case is slightly longer. Does this brass "flow" from the thick part at the base (the web), so that eventually the web gets thin and you start getting failures ?

If you neck size fireformed cases, what is it that eventually causes the case to be difficult to chamber ? Is it purely neck length, or something else further down the case ? If it is neck length, you should theoretically be able to trim each time and keep neck sizing...

Not sure if this is the answer cause I don't quite get the question but this is what a guy in a shop told me

When you fire it goes like liquid and moves forward with the gasses which is why it gets thin at the back, it flows forward. He also mentioned that using a case like .303brit that it can flow faster as there's no steep shoulder or anything to slow it down unlike an ackley improved case.

Hope that helped and is right or I've been living a lie :D

Its growing from head space and action stretch,when you bump the shoulder to get it to chamber again that brass goes up into neck.

Like a glass window is always flowing under gravity, ie thinning at the top, thickening at the bottom, Ebf make sure you store you brass up the right way to stop this process HAHAHAHAHAHA:ORLY:

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Originally Posted by veitnamcam

Its growing from head space and action stretch,when you bump the shoulder to get it to chamber again that brass goes up into neck.

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You've got some huge moment pressures in the VC. Brass is very malleable, I see the action your talking about, dont worry about it in BP cases, less pressure? but more heat

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Originally Posted by Maca49

Like a glass window is always flowing under gravity, ie thinning at the top, thickening at the bottom, Ebf make sure you store you brass up the right way to stop this process HAHAHAHAHAHA:ORLY:

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surely you just need to turn your cases every so often ? ;)

Just like a wife, feed it too much (powder in this case) and they stretch and grow, some are predisposed to stretch and grow more than others. Lesson? Don't feed them to much.

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Originally Posted by Maca49

Like a glass window is always flowing under gravity, ie thinning at the top, thickening at the bottom

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A myth, as often perpetuated as regularly as it's debunked.

Does Glass Flow? | Corning Museum of Glass

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Originally Posted by Ryan

A myth, as often perpetuated as regularly as it's debunked.

Does Glass Flow? | Corning Museum of Glass

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We'll i'll be! I always thought it to be true.
But to be fair what would a glass museum know about glass?;)

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Originally Posted by ebf

I'd like to understand the basics behind case expansion a bit better.

Assuming you have a cartridge that headspaces off the shoulder, and you are loading fire formed cases for a single rifle.

After each firing the case is slightly longer. Does this brass "flow" from the thick part at the base (the web), so that eventually the web gets thin and you start getting failures ?

If you neck size fireformed cases, what is it that eventually causes the case to be difficult to chamber ? Is it purely neck length, or something else further down the case ? If it is neck length, you should theoretically be able to trim each time and keep neck sizing...

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The brass flows forward under pressure from 50,000 psi gasses it also pushes the casehead back against the bolt the action flexes and the headspace of the case is longer, the brass being malleable springs back to it's original size as the brass work hardens from repeated firings it loses the ability to return to it's original size and you need to full length size the case, the pressure also pushes brass into the neck making it longer also some people believe that pulling the expanding button back through the neck lengthens it,
once the neck gets too long it will crimp the bullet and cause super high pressures I have seen one rifle blown up because of this,
recommend practice is to trim the case 10 thou under maximum length, After a number of firings the brass gets too hard to spring back
and needs to be annealed or replaced.

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Originally Posted by shooternz

The brass flows forward under pressure from 50,000 psi gasses it also pushes the casehead back against the bolt the action flexes and the headspace of the case is longer, the brass being malleable springs back to it's original size as the brass work hardens from repeated firings it loses the ability to return to it's original size and you need to full length size the case, the pressure also pushes brass into the neck making it longer also some people believe that pulling the expanding button back through the neck lengthens it,
once the neck gets too long it will crimp the bullet and cause super high pressures I have seen one rifle blown up because of this,
recommend practice is to trim the case 10 thou under maximum length, After a number of firings the brass gets too hard to spring back
and needs to be annealed or replaced.

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Seriously, you have personally witnessed a rifle blow up because the neck of a case was too long?

I'm struggling to believe that that was the sole case of this incident.

What were the details? ie, brand, cal etc

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Originally Posted by Proudkiwi

Seriously, you have personally witnessed a rifle blow up because the neck of a case was too long?

I'm struggling to believe that that was the sole case of this incident.

What were the details? ie, brand, cal etc

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I would have also thought it would be noticable somthing was amiss on chambering the cartridge? It would be very tight operating the bolt.

Yeah, I guess that was my point. I would think you end up needing to smash the bolt forward and down with a hammer in order to apply the pressure needed to blow an action.......along with having used the wrong powder.......and probably the wrong cal bullet.

I just dont see it happening as described........

I had a play sizing down 06 cases to 08 to find my neck length limit.

And then of course fired some at different lengths.

Tight to close bolt(on the neck) did result in high pressure,flat primer,head extrusion into bolt recesses and stiff bolt lift. From a safe working max load.
So in this case it did raise pressure but not Arse puckeringly.

Can't see it blowing a rifle up unless load is already very hot in a very overbore cal.

Tho i can think it could be worse if you were crimping into a canalure and had enough neck length to stop the crimp releasing.

But you would still notice stiff closing of bolt.
Would you notice it on a semi?

The rifle was a Weatherby Vangaurd .308 the shooter said the bolt felt a bit stiff he was only neck sizing so thought it just needed full length sizing, he had not heard of trimming cases, don't know long the case was just enough to stop the bullet releasing properly,
the gases blew out through the magazine splitting the stock the shooter collected wood splinters in his arm and brass fragments in his face luckily he was wearing safety glasses, I have read of some others happening, the only other blow up I have witnessed was an overload the shooter changed powders but not the weight and blew out a piece of the action and cracked a bolt lug, we are dealing with very high pressures, it doesn't take much to over pressure a load if proper loading practices are not followed I double check every step of the process.

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Originally Posted by Ryan

A myth, as often perpetuated as regularly as it's debunked.

Does Glass Flow? | Corning Museum of Glass

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Being an old hack and re glaze man, I have never seen a pane of glass thick at the top and thin at the bottom, I therefore conclude that the old old old hack and re glaze men used to measure the glass before installation and always put the thick end down! They created this illusion just to confuse us, who would have thought!

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Originally Posted by Maca49

Being an old hack and re glaze man, I have never seen a pane of glass thick at the top and thin at the bottom, I therefore conclude that the old old old hack and re glaze men used to measure the glass before installation and always put the thick end down! They created this illusion just to confuse us, who would have thought!

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it would be drawn sheet glass on those old hack and smack putty jobs(use to a have adrawn sheet plant manufacturing glass up north)sheet glass is quite wavey with lite on it(it does vary in thickness but that is due to the process of drawing the molten glass up at tower between rollers. Today s glass is all (new) imported float glass from over seas ,float is consistent in thickness and optically superior and easier to cut as well.we do toughen glass in Nz but not actually produce as a new product(that is stock sheets of raw annealed glass)toughened is cut to size before toughen can't cut after proccess