Case Neck Separation

D

Dave Rabin

New member
Please help me diagnose a case failure: yesterday one of my .308 cases completely separated at the neck, just above the shoulder; the neck basically just sheared off and stuck in the chamber when the case was extracted. The cut was perfect -- it looks like someone used an extremely sharp saw and made a perfect cut straight through the neck.

Pertinent data:

1. The rifle is a stock .308 Win. Savage Model 12 Palma rifle. The cases are Lapua .308 Win. Palma cases that take small rifle primers.

2. I turned the necks on the cases, but just enough to clean up the high spots, taking off maybe .0005". I cut slightly into the neck/shoulder junction as I always do, no more and no less than all other cases I've turned.

3. I FL size each time but bump the shoulder no more than .002". I size the necks in 2 passes, first with a .337" bushing in the FL die and then with a .334" bushing in a neck sizing die.

4. The case had been fired about 9 times, always with either Varget or IMR 8208 XBR. I have never exceeded the published maximum charges. When this failure occurred, it was loaded with XBR, well below maximum.

5. I annealed the cases once, about two firings ago.

6. The bullets were the Sierra 155 Palmas.

If I'm doing something wrong I want to know it so I don't repeat it. If this is a metallurgical failure of some kind, is it serious enough that I should pitch that lot of brass?

Last thought: is there any way this could have been caused by the rifle? The cut was so perfect it just doesn't seem random enough to be a failure of the metal.

Thank you.

Dave Rabin
 
Yes, with Imperial sizing die wax, including both the neck and the body. The bushings are Redding Titanium Nitride. I removed the expander ball in the FL die before the sizing, and sizing has always been very smooth.
 
The only time I have had this happen is when I cut into the neck/shoulder junction a little too much. Barely touch the shoulder (neck turning) now and problem went away.
Darn neck of the case stuck in the bushing and was a booger to get out. Hope you figure it out. Good luck.
 
Yes, that cut into the shoulder was probably too far. Are you crimping the bullet? If so, it may have been held so tightly that the case neck failed. I NT the same way on all my brass but I never crimp the bullets in 7 different bolt guns. No separations.
 
That clean break you describe is typical. If you have had success with previous "sets" of cases I would suspect that you did something diferently with the current batch that you didn't realize. There's no reason to cut into the shoulder unless the bullet seats into that area and even then it might not be necessary. The remainder of the cases will follow in a couple of firings so toss them now before another bites the dust. Save a few for making dummies.
 
Also, if your cases are not exactly the same length, the stop on the neck turner will make the cut deeper into the shoulder on the shorter cases. Stand the neckless case next to a normal case (or measure) and see if the separation is exactly at the shoulder junction cut. Does your seater crimp the bullet?
 
Guys,

Thank you for your help. I'll just prep another batch of cases, and stop short of the shoulder. The boattails on these bullets are so long that the bearing surface of the bullet is in contact with the neck only for a short distance below the mouth anyway. And no, I don't crimp them.

Thanks again.

Dave Rabin
 
Just remembered! I had a neck/bump die that had a different angle in the shoulder dimension. The angle was such that the contact was always at the neck shoulder junction and rather than a bump die it was a bend die. This die caused necks to come off - in the die - same die.

That was when I had the idea for the "Nek Nokker" that Charlie Hood so gracioulsy made for me.
 
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