Case head separation and collapsed shoulder

[Purple shoulder]

I've had a couple case head separations over the years but never had one with a dented shoulder like this. I assume the neck made a good seal and the pressure escaping from the crack to the outside of the case then forced it in. Is this what happened here?
The case is a Federal. I'm not sure of the case history as it may have been some range brass. I do check for incipient case separation but I may have missed signs on this one.
A proven load in my gun Ruger M77 300 wm 80 grains H1000 Hornady 178 grain A-Max
This case did have an ejector stamp on it which I haven't seen before with this load.

 

[b72471]

I have had this happen on another caliber and my guess would be a brass that had the beginning of head seperation before it was loaded that last time. Sometimes we overlook or simply don't notice, and on the last firing the head seperates easily and causes the shoulder to implode as seen in your picture. When this happens it's a good idea to take a very close look at all brass from that lot, if unsure discard all brass from that lot.
enjoy.

 

[Ron AKA]

I have seen the dents before, but they were not associated with a head separation. I was working up loads for a ladder test and got sucked into using the current Hodgdon loads for a 140 grain in my .264 WM. They are wrong, and way too light. I believe Hodgdon has interchanged the loads for the 160 grain with the 140 grain. Heaven help someone who uses those 160 grain loads. I wrote Hodgdon about it, but they don't seem to care. In any case it was an excessively light load of H4831. I think perhaps combined with necks that were work hardened and really needed annealing, the necks didn't expand and seal, and the gases on the outside of the case collapsed the cases almost identically to yours. See this photo of the three lightest loads.

Since yours was associated with a head failure and wasn't a light load, I would agree with your conclusion that the external gas pressure came from the failure crack. That area up near the shoulder probably has the thinnest brass and is the first place to give in -- the same as mine.

These cases may have been damaged before you got them, but I am convinced that the cause of case head failures is over sizing with a full length die. One needs to be careful to only bump the shoulder 0.001" and not do a full stroke resize. In fact I have been able to only partially resize about 65% of the neck, and reload the case. That is probably the best way if you can get away with it. Or if you have a neck sizing die, just size the neck.

 

[bigedp51]

I've had a couple case head separations over the years but never had one with a dented shoulder like this. I assume the neck made a good seal and the pressure escaping from the crack to the outside of the case then forced it in. Is this what happened here?
The case is a Federal. I'm not sure of the case history as it may have been some range brass. I do check for incipient case separation but I may have missed signs on this one.
A proven load in my gun Ruger M77 300 wm 80 grains H1000 Hornady 178 grain A-Max
This case did have an ejector stamp on it which I haven't seen before with this load.

The secret to not having case head separations.

1. Don't use range pickup brass of unknown origin.

2. Only bump the case shoulder back .001 or .002 and don't let the case headspace on the belt.
Most belted magnum dies when adjusted per the instructions will push the case shoulder back too far. And this creates too much head clearance or air space between the rear of the case and the bolt face. And this allows the case to stretch excessively when fired and causes case head separations.

 

[Purple shoulder]

I have a homemade tool for measuring how much the shoulder gets pushed back. I try to keep it minimal but I will be paying close attention to this in the future. Thanks for the input guys. ☺

 

[Ron AKA]

I have a homemade tool for measuring how much the shoulder gets pushed back. I try to keep it minimal but I will be paying close attention to this in the future. Thanks for the input guys. ☺

With my 6BR I was using the Forster Bushing Bump die to actually measure how much I was bumping. The fired case has clearance in the body and sits against the shoulder so you can use the die itself with a vernier to measure base to shoulder distance. But I finally broke down and bought Hornady bushings to measure it in a more convenient way. Not all that expensive as I had some of the parts already which I was using to measure length to the bullet ogive. X-Reload sell individual bushings if you can't justify buying the whole set.