Help Please. Case Head Separation.

[bigdawg86]

Hey guys so I am a bit perplexed. I just got a new scope mount and just back from zeroing in my LR308 in 6.5 Creedmoor. The rifle was initially zeroed with 120g spitzers and was shooting subMOA once dialed in. I then switched to 140g bullets to get my final zero and my first shot was a case head separation. That ruined my day haha...The fired round clocked 2680FPS, so judging by velocity it wasn't a hot round, and I have shot hundreds of rounds at 40g with that bullet. I was planning on getting a zero and readjusting my gas block once dialed, but never got a chance to.

Load data as follows:

Brass: Virgin Hornady (purchased here from Calgunner) ONCE FIRED THROUGH MY RIFLE
Primers: WLR Magnum
Bullet: Barnes Match Burner 140g
Powder: 40g IMR 4451
Barrel: 24" Lilja
Gas Block: Seekin's Adjustable
BCG: JP LMOS with HP Bolt

There are two differences from my prior loads and that is today was virgin Hornady brass, and the primers were magnum which was on accident. I have never noticed pressure differences from brass to brass or regular vs magnum primers so am having a hard time believing that would cause this catastrophic failure... I know they CAN make a difference, but again catastrophic??? The primer was flattened / ejected. So by the photos of the case I would say it was a hot round, but the FPS and fact that I have shot the near identical load hundreds of times tells me otherwise.

I pulled a few rounds and powder was indeed 40.0g and was +/- .1g
I compared the powder in the case to the 4451 and they check out as same.

I really am not sure what to make of this as this has never happened to me before and would appreciate any guidance.

[highpower790]

OP, do you know what kind of rifle the brass was fired in before you picked it up,and what kind of die are you using? ok
I see virgin brass listed.
My guess is that you didnt size the virgin brass causing the case to stick a little at the case head and with the magnum primer,when fired the case separated.

[bigdawg86]

I did only neck size these cases as they fit fine in my Wilson case gauge .

[highpower790]

I did only neck size these cases as they fit fine in my Wilson case gauge .

Is there anything special about the chamber?,you're using a Lilja barrel .the chamber dimension at the case head may be different.

[bigdawg86]

Is there anything special about the chamber?,you're using a Lilja barrel .the chamber dimension at the case head may be different.

Nothing special. My rifle usually loves factory Hornady ammo so I don't see how this would be much different. I JUST REALIZED I WAS SHOOTING MY ONCE FIRED BRASS

Only non ammo related variable is my gasblock ran the 120g great, but may be overgassed with 140g

[JagerDog]

Pressure doesn't cause case head separation. I got nothing else.

[bigdawg86]

Pressure doesn't cause case head separation. I got nothing else.

Fair enough lol...

[Rusty Scabbard]

Possibly a timing issue ?
second pic shows a flared out edge if the ejected shell base. Maybe it had some pressure behind it when it left the chamber ? It seems to make sense with the additional info of the blown out primer and shooting a heavier projectiles than before.

[smoothy8500]

I did only neck size these cases as they fit fine in my Wilson case gauge .

Maybe you didn't see this note at the bottom of the instruction page:

Note: Does not measure body diameters. This gage is intended to be used with fired cases to determine a basis for full length sizing and trimming.

Also is in the description fro the website

https://lewilson.com/case-gage/?gclid=EAIaIQobChMIxorpqvP44AIVaP7jBx0kmQhoEAAYASABEgIhLfD_BwE

Regardless, most reloaders for semi-autos use full-length dies. Usually, the separation comes after a few reloads. More prevalent when the sizing die is set too low and causes cases to stretch on firing.

[Rusty Scabbard]

......

Regardless, most reloaders for semi-autos use full-length dies.

Because an out of battery touch off would really suck !
Always full length resize for autoloaders.

[bigdawg86]

Because an out of battery touch off would really suck !

Always full length resize for autoloaders.

So Honestly I kinda forgot what I did with these rounds until I started writing about it... For the record I did full length size WITH a bushing die.

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[tawadc95]

Pressure is one of the reasons for case separation, albeit indirectly.
Unsupported pressure.

The rim looks like it had a tear from hitting the ejector.
The separation appears to be above the case web, higher than normal.
Im guessing the shoulder was set back a bit far...I think between the indent and tear at the rim and the missing primer you had a headspace problem. To me that explains the case separating higher up at a weaker place than the web where insepient separation first appears.

I don't think it would be out of the realm of possibility to have a bad case from the factory, we are pretty accustomed to consistent quality and trouble free supplies which makes us wonder what We did wrong and never consider other possibilities beyond our control.

Have you fired it since?

[bigdawg86]

Oversizing may be possible... As I am using Whidden dies which will grossly over size if you set to contact shell holder like "normal" dies. I know for a fact I had a few that seemed oversized before I settled on a acceptable size. Unfortunately I didn't mark the short cases and this very well could have been one.

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[dadswickedammo]

The separation is higher then the norm..
It would appear the shoulder is was bumped back to far. Your volosity is in the range but just imagine the undersized cast in the chamber sending the bullet slamming the case head into the bolt flattening the primer and the shoulder being forced forward at the same time pulling the case apart.
I would say bad head space but factory ammo is GTG.
So it really can only be the shoulder to far back.
I have done this in a 303brit.

[ar15barrels]

I did only neck size these cases as they fit fine in my Wilson case gauge .

It's more important that they properly fit your gun than a case gauge.