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Case head separation and where I stop when partially sizing.That

3K views 12 replies 5 participants last post by  accident 
#1 ·
I'm sitting here at my bench sizing some 300 win mag cases. I just ran into something I thought I would share, a case head separation. I tumbled this particular batch of cases about a week ago. I tumble first to remove some of the carbon from the neck. As I was lubing the cases I found the case head separation. Inspecting your cases are vital!! That's the problem with belted cases right? 2-3 loadings and you get a head separation. Well, not necessarily. This batch of cases have been loaded and fired 15 times and I don't load light charges. They're not max, but they're close to it. Case failures happen. It's inevitable, whether it be in the form of a neck split or a head seperation. That's one of the benefits of partially sizing your cases. I don't bump my shoulders the recommended .002-.003". In fact, I don't even touch the shoulders. Here are pics of the head separation and of a case that was just pulled from the sizing die.


 
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#2 ·
Your post is interesting. Not bumping the shoulder should assure the case is the maximum length to fit in the chamber. Most belted magnum cases separate because the case headspaces off the belt and most belted magnum chambers are too long. The result is the case stretches with each firing to fill the chamber. Then when re-sizing, the case the shoulder is pushed back. 3 or 4 cycles and you get head separation.

But your case is different since you have headspace off the shoulder. So there should be minimum stretching of the case body . So why is there head separation?

Is it because the guns bolt moves reward during firing making the case stretch? Is it because the receiver of the gun stretches and allows the case to stretch? Admittedly you got lots and lots of reloads from these cases but I would not expect this failure type. Non-belted cases reloaded this many times usually die from a burn through of the case neck, in my experience.

If you partially re-size a case body the shoulder is moved. The correct way to do it is with the case gauges as sold by RCBS. Measure up fired case and incrementally partial size until the case gauges tell you when you have reached the fired case dimension. Could it be that you need to use a true neck sizer, rather than a regular sizing die that does change the shape of the case body even when you don't let it touch the shoulder????

While not a serious problem, normal reloaders will never see it. They will only get 3 or 4 reloads out of their cases. It is curious what is happening. Have you figured it out yet?

LDBennett
 
#3 ·
At this point, I'm still not sure why the case failed where it did. The bolt lugs are fine. The headspace is good. This is the first head separation I've had with this rifle. Perhaps the case was weak there from the start? I don't know if an actual neck sizing die would be better. A fired case is only expanding .001-.0015 larger than a sized case.
 
#6 ·
I've found that belted cases usually have short case life. That you've reloaded some cases 15 times is exceptional. This is even more so because you say you load your rounds on the 'hot' side.

On the cases that have lasted so long - are they a different brand than the one case reloaded 3 times? Another thing: firing hot loads is hard on the action and bolt. Maybe a good idea to take the rifle to a gunsmith and have them use gauges to check the headspace just to be sure the action hasn't stretched a bit. This will cost a little, but it will give you peace of mind that your rifle isn't on the verge of failure.
 
#7 ·
The idea to get long case life on a belted magnum case is to get the case after the first firing to headspace on the shoulder not the belt. At the first firing the chamber is filled by the fired case. Normal full length sizing pushes the should back. This works the brass with every firing. That is why the only last 3 or 4 reloading. slayer adjusted the sizing die up so that the shoulder was not touched by the sizing die. But I don't know exactly how he did it.

If case gauges were not used then the little bit of sizing done to not touch the shoulder does not assure the shoulder is not moved. You have to use case gauges (like those from RCBS) to verify the should ends up the same distance from the head of the case to the shoulder. Just adjusting the sizing die up is not good enough for perfection. slayer may have done it right (??) in which case I think something else is at work here. Cases for rifles don't normally have case head separation as a failure mode unless their is a head space issue. The have burn through in the case neck, in my experience.

So it is now a mystery until we get more info from slayer.

LDBennett
 
#8 ·
This particular batch of cases are mixed brands. The majority of it is a brand that most everyone complains about, Federal. I find federal cases to be about the best for longevity for belted magnums. There are a few R-P cases in there and a couple Winchester. The head separation was a Winchester case. Since they no longer make their own cases, it's hard to say who actually made it. I also discovered 4 neck splits in this batch. 2 federal and 2 R-P. I did put a piece of masking tape on a case(I know, not very scientific) and the bolt would not close. At this point I still don't believe there's a headspace issue. I do have a friend who is a semi retired 'smith, so when I get time I'll have him check it out. This particular load is 1.3gr below alliants max. The rifle has only ever had 6 book max charges through it. No ejector marks or blown primers ever.
My method for ensuring the shoulders aren't touch is to use a sharpie to color the shoulders. I run the die down to size the neck without removing marker from the shoulder. If any marker is removed, I back the die out and run a different case. I have 2 sets of dies for two of my 3 belted magnums. I set to not touch the shoulder and one set to bump the shoulder back enough to allow easy chambering if/when the cases get hard to chamber.
As LD pointed out, the necks should be where the cases fail. Why this particular case failed where, I'm still not sure. The only logical thing I can think of is, the case was thin in that area from the beginning.
 
#9 ·
slayer:

It is really hard to complain when you get 15 reloads from the case. The first firing had the case headspace on the belt. That may have weakened the case just above the head. It took 14 other excursion through your gun before it gave way.

But I still think the right way to not move the shoulder back using a FL sizing die is with RCBS case gauges. I have used them often enough to know that as you progressively move the die down to approach the shoulder the sizing of the body pushes the rest of the case around. I see this as shoulder movement. I don't get it right until most of the body of the case is sized. I actually push the shoulder back a couple thousandths. While your system apparently works (15 reloads before failure) there may be a bit of room for the shoulder to move during firing....even more than my couple thousandths. without good measurement you don't know for sure.

If the gun has excessive headspace (from the bolt to the belt) then the case still has to stretch to reach the bolt face. If the gun checks out then re-think your method of sizing or just kiss it off. 15 reloads is a lot to expect from any case. I never see that many reloads in any of my rifles before something in the case fails or get shaky.

LDBennett
 
#13 ·
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