Thread: 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

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

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.

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

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

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.

Originally Posted by Maca49

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

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

Does Glass Flow? | Corning Museum of Glass

Originally Posted by Ryan

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

Does Glass Flow? | Corning Museum of Glass

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

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...

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.

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.

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

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

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?