9mm Case Head Separation

I have had an issue that looks like your photo when using clean cases with dry Hornady dies.

The issue turned out not to be the dies so much as the lack of case lube. The carbide ring (which is a different material from other die brands) apparently is (or was in my case) gripping the brass and physically moving it toward the case head in a very slight, but noticeable way. The "ring" is the result of the die not being able to "size" the entire case due to the shell plate holding the case rim.

In my situation the cure was to start using Dillon case lube. This is a lanolin and alcohol mixture that can be used immediately after application. Lanolin is a well known extreme pressure lubricant.

I would not fire that case in a chamber that wasn't fully supported.
 
Palladan44 said:
Are you also positive these are all from the original same batch of once fired (or new) cases? I've came across a bunch of one-offs in my single batch brass over the years.

Even if not, they usually fail one at a time.
Ever notice cracked cases usually manifest themselves one (or 2)at a time?

Just toss it, and move on. I'd say you're just fine to continue loading your others.
You monitor your brass probably better than most, you've proven that. Carry on and don't let this make you flinch and start jerking your shots wondering if you've got an imminent CHS on deck!!! LOL.
Click to expand...
I don’t need an excuse to flinch unfortunately:)

All I know about the case provenance is from May/June to present. I arbitrarily grabbed a bunch from my Winchester container. Anything before that is a crap shoot. Yes, I know, not a scientifically sound method.

Thanks for the advice
 
1000004218.jpg
Here's where I think you're at with this particular "case" ^^^^ We keep pounding the Y-axis but let's not forget the X-Axis, for the X-Axis carries more weight!!! Let's not forget about the World of Pain that awaits if we push limits. In the rest of the human safety world, we aim for a safety factor of 10x.
By continuing to load in your 12x reloaded cases you are probably below that factor.
$ 161.50 for a thousand pieces of Starline shipped, in stock now.
 
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You are making much to do about nothing or a Mt out of a mole hill. Its a piece of 9mm . Brass does not last forever. Sometimes it splits, cracks separates or folded spindled and mutilated.

It could be the brass maker, some will swear never to use that brass
Could be the die, if it was Lee then that is the reason,
Could be the cleaning method, to much acid and it weakens the brass
Could be the powder, primer, those all suck
Maybe it was the reloader?

Or it could just be the brass is old and tired.

It is a New Year, throw it away and move on.:D
 
Rule3 said:
You are making much to do about nothing or a Mt out of a mole hill. Its a piece of 9mm . Brass does not last forever. Sometimes it splits, cracks separates or folded spindled and mutilated.

It could be the brass maker, some will swear never to use that brass
Could be the die, if it was Lee then that is the reason,
Could be the cleaning method, to much acid and it weakens the brass
Could be the powder, primer, those all suck
Maybe it was the reloader?

Or it could just be the brass is old and tired.

It is a New Year, throw it away and move on.:D
Click to expand...
Ouch! The waste!

A thousand generations of Scotsmen just screamed in horror! 😱

🤣😉
 
It would be difficult to have a case head separation in 9MM, simply because it’s a straight (taper aside) walled case.

Same with .38 Spl, but I have a pic where one of our members managed it. Very high pressure.

What @rfwobbly said about his sizer and brass could be what happened in 9MM I guess, but I have never had an issue and have tried 4 different 9MM sizers.
 
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After reading back through this I realize I wasn’t clear and the picture doesn’t show the case is actually cracked completely through about one third of the circumference. It wasn’t a bulge per se or discoloration. It was a crack. Some of your responses indicate my lack of clarity.

So, now I’m thinking this is a case that simply gave up the ghost. Was just worn out. Maybe prematurely due to the undersize die, maybe not.

I’m going to continue shooting from the same Winchester only batch I’ve been using and for the duration will use a standard sized die vs undersized.

This being my first case failure of this type had me spooked. Thanks for walking me back from the edge. Appreciate the expertise.

The below picture is of three undersized primed cases on the left and three regular on the right.
IMG_4447.jpeg
 
CQB45ACP said:
After reading back through this I realize I wasn’t clear and the picture doesn’t show the case is actually cracked completely through about one third of the circumference. It wasn’t a bulge per se or discoloration. It was a crack. Some of your responses indicate my lack of clarity.

So, now I’m thinking this is a case that simply gave up the ghost. Was just worn out. Maybe prematurely due to the undersize die, maybe not.

I’m going to continue shooting from the same Winchester only batch I’ve been using and for the duration will use a standard sized die vs undersized.

This being my first case failure of this type had me spooked. Thanks for walking me back from the edge. Appreciate the expertise.

The below picture is of three undersized primed cases on the left and three regular on the right.
View attachment 1187076
Click to expand...
Wow! That's really really bad!
One time I ran a 9mm case on a 38/357 resizing die and it looked just like the piece of brass in question on the top of your picture.
 
I can't see inside the case, but the outside looks like a sharp entrance to a carbide sizer,
which exacerbates its self when you size way down at the solid head/case wall junction.
I have two carbide 9MM sizers that will do this, and since the case is tapered, that makes
it look worse as well. Sizer needs to be tight enough at the case mouth, but that can
make it too tight down near the base. My Lee carbide sizer with the long tapered insert
does not do that.

What does the inside look like?
Are you just feeling the change between the solid case head and where the case wall starts?
index.php
 
Walkalong said:
I can't see inside the case, but the outside looks like a sharp entrance to a carbide sizer,
which exacerbates its self when you size way down at the solid head/case wall junction.
I have two carbide 9MM sizers that will do this, and since the case is tapered, that makes
it look worse as well. Sizer needs to be tight enough at the case mouth, but that can
make it too tight down near the base. My Lee carbide sizer with the long tapered insert
does not do that.

What does the inside look like?
Are you just feeling the change between the solid case head and where the case wall starts?
index.php
Click to expand...
Not quite sure of the question. Clarify please and I’ll answer. I know I’m dense.
 
I had an undersized die that made an ugly spot down at the bottom like that, entrance to the carbide sizer plus being tight at the case head all combined to do it.
 
Palladan44 said:
How do you know which is which?
I have a dillon 9mm carbide die, and it seems undersized. I'd like to get one that resizes slightly less, so what are my choices?
Click to expand...
If you mean the cases, I keep them in separate mtm boxes.

If you mean the die, there’s a “U” where normally the caliber would be.

We had a thread a couple months ago on these dies and I posted verbiage from Dillon indicating some of their dies were undersized.

edit: mine are Lee btw

IMG_4449.jpeg
 
The crack might have occurred when the shell holder pulled the case out of the U die. I’ve been experimenting with the 9mm U die and it takes a lot more force to insert and extract the brass.
 
enjoyed this post, pix of one that happened to me, 9mm Commander that i've shot many times. looking at it carefully i see a crack on the other side. guess its just was shot to many times. put another 100 thru it to be sure and no problems.
 

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