Thread: Case head separation imminent

Case head separation,what to look for and how to avoid it comes up fairly often on here so when prepping some of my "beater brass" today I found one and thought I would section it to show what to look for.


A line in the brass just above the case head web, often this is not perfectly symmetrical and can't usually be felt on the outside.
Feeling down inside the case with something like a paperclip bent 90degrees at the bottom you will generally feel the groove.


So what causes it and how best to avoid it?
First we need to understand what is happening when we pull the trigger.
The firing pin drives the case forward in the chamber until it is stopped by usually the shoulder of the case or the belt/rim contacting the corresponding part of the chamber.
This creates a space between the case head and the bolt head called "Headspace"
Now that the case can no longer move forward the primer is detonated and pressure in the case begins to build.
As pressure builds the thinnest part of the case at the neck expands to grip and seal off the chamber and release the projectile.
The rest of the case body expands and is held by the chamber but the rear of the case thickens near the case head till it can no longer stretch out to the chamber and as pressure continues to build to peak this part of the case is stretched rearward until stopped by the bolt.
This stretching happens in the same place every shot and no resizing method will put that brass back where it came from.
The greater the Headspace the greater the stretching with each shot.
When rezising that extra brass is squeezed in and up and the case gets longer....If you have to trim brass often you probably are over sizing the case.

Most full length Sizing die instructions tell you to wind the die down to the shell holder and then + another 1/4 or 1/2 turn.
This will produce normally brass that should chamber in most rifles of that chambering.
That means for a great many the brass is sized much shorter than necessary.
One way to set up your die to minimize headspace and brass stretching is to measure fired brass to a mid point on the shoulder and start with the die half a turn up and size and wind down the die until you get a sized shoulder measurement that is 1-2thou of an inch less than the fired case.
Another way to go is the same thing but chambering the case and sizing till the bolt just closes with little or no resistance. This will minimize headspace and case stretching and give your cases a longer life.
So also will neck sizing only but at some point usually you will have to full length size again.

Good work
Its called science and I like it

Nice and informative thank you sir

How many times has that case been reloaded vc???

What's the likely outcome if it separates when fired?

You "sleeve" the chamber and can either take pride in having just designed a new wildcat that you will need new brass for or you fish it out. Either way shooting stops for a while.
A pull through/ bore snake run down from the muzzle can often get the split case out.

Originally Posted by Marty Henry

You "sleeve" the chamber and can either take pride in having just designed a new wildcat that you will need new brass for or you fish it out. Either way shooting stops for a while.
A pull through/ bore snake run down from the muzzle can often get the split case out.

Thanks Marty, so no real health hazard? Just an inconvenience?

Originally Posted by Gibo

What's the likely outcome if it separates when fired?

A stuck case and possibly a bit of gas back in your face

Originally Posted by matagouri

How many times has that case been reloaded vc???

Unsure... probably at least 10 times and in 4 different rifles.
It's my "Beater" brass I don't care if I lose so use for bush loads and start of load developments so has had a hard time in more than a few 308s

I had twice fired hornady brass doing this to prob 5 out of 10 casings

Originally Posted by Gibo

Thanks Marty, so no real health hazard? Just an inconvenience?

Some rifles that don't have good gas safety features can make it a nasty experience, modern well-designed bolt actions that divert a lot of the gas away or trap it in the action you might not even realise it.

Good section and write up - possibly worth while adding that with a lot of cases if they are fired in a rifle they'll chamber back in the same rifle quite happily. In that case it's a little bit hard to use the 'until it doesn't chamber' thing to guide your headspace setup. I prefer the method of marking the case neck and shoulder and running the case into the die until the marks are just touching the case's shoulder. Then you should be just bumping the neck back on each sizing...

Originally Posted by No.3

Some rifles that don't have good gas safety features can make it a nasty experience, modern well-designed bolt actions that divert a lot of the gas away or trap it in the action you might not even realise it.

Good section and write up - possibly worth while adding that with a lot of cases if they are fired in a rifle they'll chamber back in the same rifle quite happily. In that case it's a little bit hard to use the 'until it doesn't chamber' thing to guide your headspace setup. I prefer the method of marking the case neck and shoulder and running the case into the die until the marks are just touching the case's shoulder. Then you should be just bumping the neck back on each sizing...

Could you put up some pictures of the marked cases before and after please

Originally Posted by Gibo

Thanks Marty, so no real health hazard? Just an inconvenience?

Not as bad as finding out you have a head case problem...

Originally Posted by Padox

I had twice fired hornady brass doing this to prob 5 out of 10 casings

You must have had very large headspace and or chamber dimensions to get that on only two firings.