Thread: Case head separation

Here's a couple of photo's that are quite good for showing the cause of case head separation. The case is I think a .308 win, with the characteristic groove just in front of the area where the web of the case head would finish...

Probably not something a lot of people have seen so worth chucking up the photo's I thought.

And the cause?
Setting the shoulder back too far when full length sizing. Easily avoided.
GPM.

Here's one about to go.

Found that one on the range, probably likely to be a reloaded case but didn't see the other end and don't know the history to confirm.

Interesting my 270 is doing this thought it was a head space issue

Originally Posted by Padox

Interesting my 270 is doing this thought it was a head space issue

Greetings,
It is a headspace issue created by setting the shoulder back too far when full length resizing by having the die down hard on the shell holder. Will post further on this tomorrow.
GPM.

Oh goodie the partial length debate shall kick off again lol. My nosler manual has a great photo showing its mechanics,I've posted it on here before.

Well "partial" doesn't accurately describe the approach. It would be better to say correct or appropriate headspacing.

The method doesn't necessarily require shoulder gauges. Start by dismantling or at least fully unwinding the spring tension in the bolt. Starting with too little sizing on a case that is slightly tight after firing, slowly wind the die in until the bolt will close with basically no resistance on bolt closing. This will get a more correct amount of resizing. Eric Cortina has a video on it from memory.

Greetings to all and thanks @Micky Duck,
My old Nosler no 1 Manual (1976) details the options of neck sizing, partial sizing and full length sizing in some detail so I won't repeat it. Neck sizing works well with light loads and partial sizing can work well with sub max loads with the more tapered cases. Full length sizing as defined by Nosler is where the case is returned to Factory dimensions for easy chambering. The problem lies in the tolerances for the dies and chambers. The gold standard for the set back of the case shoulder, when full length sizing, seems to be 0.05mm (0.002"). Only one of my sets of dies produces this result and only in one rifle. Generally the shoulder will be set back more and with some dies a lot more. This creates the excessive headspace that results in partial or total head separation as shown in the photos earlier in this thread. The fix is not to set the shoulder too much. To do this you need to be able to measure how much you are setting the shoulder back. Hornady sells a kit for this called a Headspace Comparator. This clamps onto the lower jaw of your callipers and lets you measure the case length to a point on the shoulder. Comparing the length of new, fired and resized cases can be a humbling experience but at least we will know how big the problem is. As I found setting the die down hard on the shell holder almost always over sizes the cases. You can carefully adjust the FL sizing die to achieve the right shoulder setback but my results with this have been variable. The deluxe solution ,with a deluxe price, is the purchase of a set of the Redding competition shell holders. These allow you to set the headspace of your cases to match your chamber with some precision.
For my loading I neck size for my old soldiers and light target loads in my .308. For full power loads for longer range target shooting I use the Redding Competition shell holders. I also check for the groove developing on the inside of the case with a bent wire paper clip at each loading.
Regards Grandpamac.

Originally Posted by 6x47

Well "partial" doesn't accurately describe the approach. It would be better to say correct or appropriate headspacing.

The method doesn't necessarily require shoulder gauges. Start by dismantling or at least fully unwinding the spring tension in the bolt. Starting with too little sizing on a case that is slightly tight after firing, slowly wind the die in until the bolt will close with basically no resistance on bolt closing. This will get a more correct amount of resizing. Eric Cortina has a video on it from memory.

or to put it another way...you place resizing die in press as per normal but instead of winding in the extra 1/3---1/2 a turn you back it out 3 turns..... put fired case in shell holder and move handle as normal....remove case and try in rifle...still tight..so screw die down half turn and go again...keep doing this till bolt closes with no risistance....yes the bench shooting guys like a LITTLE resistance but for me,for hunting,I like it to shut with only tiniest hint of resistance if any at all..nothing worse than hunting all day and having big fat deer looking and laughing at you fighting to get bolt shut on oversized round!!!!
set the locking ring on die,dont forget to tighten wee grub screw....try another half dozen cases to make sure you have got it right....and leave the plurry thing alone from then onwards.
the ONLY time my .270w dies get moved is the seating die if using my 170grn fence posts..cannot unscrew top enough so have to back die out to seat them long enough to be happy.
if wanted I will take photo of the picture/diagram if some one wants it...

Greetings @Micky Duck,
The .270 has a more tapered case and a shallow shoulder angle and, as you found, works well with partial sizing as long as the load is not too hot. In my .308 I had mixed results so went to neck sizing and more recently the competition shell holders for the hotter loads. I still neck size for the light short range (100 metres) target loads in the .308.
Greetings also @6x47,
Partial sizing and appropriate head spacing are actually different. Partial sizing is where the die is backed out sufficiently that the shoulder is not set back at all. The body of the case is reduced but only most of the neck is sized. It only works where the shoulder is at a shallow angle. I suspect that the shoulder is set back a little on chambering, not for 30 degree shoulders.
Regards Grandpamac.

I keep this handy for when adjusting dies in my note book.

On the back of Grampamac's advice above I measured all of my shell holders and there certainly is a lot of variation especially between the Hornady and Lee versions, so I have incoming a set of 5 Hornady shell holders for all of my H dies and will be more careful about which one is used with each die set. And I may start to save for the Redding competition set as well. You can always learn something no matter how long you have been doing it!