Case separation.

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Greg S

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Loaded a couple dozen 308 win cartridges for some range shooting. Not after great speed or anything, just plinking. All the same charge, every one measured and well below book maximum. Four or five of them had case separation about half an inch up from the rim. Primers weren't particularly flat and no pitting of the firing pin strike. It was mixed brass that had all been reloaded more than once but looked good on inspection prior to loading. I specifically look for a stretch, stress marks near the rim showing deterioration. Some of the brass was Norma, fired about 4 times and some was Federal fired about 6 times.

I suspect over pressure due to the crimp. Could this cause it with a below max powder charge? I'm using a Lee crimp die on 150 grain spire points with no canullar. Can't really tell by looking if the crimp is tight, loose or in between. Can the crimp really be tight on the smooth side of a bullet when there's no canullar?
 
This was happening with my buddies old savage .308. Incipient case separation. You could see a sight ring around the cases before they would separate. Not sure what was causing it though but it does have excessive head space.
There was a really good thread on it though with tons of info. Not sure how far back in the reloading forum you'd have to look.
 
You're over sizing the cases, or perhaps to view it another way normally sizing the cases and firing them in a long chamber. Either way the cartridges are much shorter than the chamber and stretch on firing to fill the chamber. The case stretches right in front of the web where the brass thins down. Then you size them too much again and repeat. Do it a few times and they part. Sometimes you can see it coming and sometimes you don't.

You can check your surviving cases with a bent and sharpened wire, (I use a dental pick) but if you are getting 20% separations chances are they are all junk now.

Do a search on incipent separation and partial full length sizing and you'll find more than I could type in a year.
 
We could see the ring around the cases and knew they were going to separate. I believe he adjusted his dies to solve this issue. I'll ask him later.
 
emerson said:
F/l sizing for a semi or lever?
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Full length resizing for a Savage 99 lever in 308. I've shot a few hundred rounds out of her which is why this brass has been reloaded before. I haven't had case separation before. I'm using RCBS dies and crimping with the Lee crimp die.

I only have one 308 so these are always going into the same gun. From reading I've done I gather I don't have to size full length each time but how do I just neck size? Different die I suppose. And why haven't I had the issue before when some of this brass has been reloaded more times. The Norma brass has been used the least and I thought it was the best quality yet it was 2 of the failed pieces.

As the gun is a few years old (1958) and I've had her for for over 30 years, I took her to a gunsmith I know a couple years ago to check headspace and general checkup. Clean bill of health and headspace is good.
 
My buddy stated using a neck sizing die and his problems went away. He put a projectile in a empty case and chambered it, I don't think it even moved.I think it's a savage mohawk
 
Since head space checked out ok then it's just case stretch from firing and full length re-sizing more than a few times. For my bolt action .300 Win. Mag. I neck size only and get several reloads from cases. I don't think I've tossed one yet due to incipient case head separation.

Full length re-sizing is recommended for lever actions.
 
As suggested, I search incipient separation and spent the last while reading CGN knowledge on the subject. Thanks everyone! No mention of neck crimp being involved.
 
Short case life is not unusual in the Savage 99. Compared to a front-locking bolt action, the action is less rigid, which makes for more case stretching.

If you want to try neck or partial sizing, the full-length sizing die you already have can be used by backing off the die until it only sizes the case just enough to chamber.

Head separations are not likely to cause catastrophic failure, but there is a risk of getting the front part of the case stuck in the chamber.

Crimping is not causing your case separations, but it isn't something you need to do. Neck tension alone should be sufficient to retain the bullet.
 
Greg S said:
As suggested, I search incipient separation and spent the last while reading CGN knowledge on the subject. Thanks everyone! No mention of neck crimp being involved.
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Greg S

I have a Lee full length Lee die that will push the case shoulder back .011 shorter than the chamber length (headspace length) if the die makes hard contact with the shell holder. This is where the ".002 shoulder bump" you read about comes into play and why a Hornady cartridge case headspace gauge is nice to have. You measure your fired case with the Hornady gauge and then adjust your die to only push the shoulder back .002 shorter than its fired length.

The problem is we live in a plus and minus manufacturing world and no two chambers or dies are exactly the same. Meaning you should set up and adjust your dies so your full length resized cases are a custom fit to "YOUR" chamber and approximately .002 shorter than their fired length after sizing.

Bottom line, the full length dies instructions are to make sure the resized case will fit in any chamber. BUT many times this over resizes the case and leaves too much room for the case to stretch when fired. And this causes case head separations by allowing the case to stretch beyond its elastic limits.
 
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Dogleg said:
You're over sizing the cases, or perhaps to view it another way normally sizing the cases and firing them in a long chamber. Either way the cartridges are much shorter than the chamber and stretch on firing to fill the chamber. The case stretches right in front of the web where the brass thins down. Then you size them too much again and repeat. Do it a few times and they part. Sometimes you can see it coming and sometimes you don't.

You can check your surviving cases with a bent and sharpened wire, (I use a dental pick) but if you are getting 20% separations chances are they are all junk now.

Do a search on incipent separation and partial full length sizing and you'll find more than I could type in a year.
Click to expand...

bigedp51 said:
Greg S

I have a Lee full length Lee die that will push the case shoulder back .011 shorter than the chamber length (headspace length) if the die makes hard contact with the shell holder. This is where the ".002 shoulder bump" you read about comes into play and why a Hornady cartridge case headspace gauge is nice to have. You measure your fired case with the Hornady gauge and then adjust your die to only push the shoulder back .002 shorter than its fired length.

The problem is we live in a plus and minus manufacturing world and no two chambers or dies are exactly the same. Meaning you should set up and adjust your dies so your full length resized cases are a custom fit to "YOUR" chamber and approximately .002 shorter than their fired length after sizing.

Bottom line, the full length dies instructions are to make sure the resized case will fit in any chamber. BUT many times this over resizes the case and leaves too much room for the case to stretch when fired. And this causes case head separations by allowing the case to stretch beyond its elastic limits.
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The above two explanations are correct. Set your die to push the shoulder back .001" to .002", and your problem will go away. The cases that you've already used will already have a reduced life, but any new brass will last a normal amount of loadings. The (unnecessary) crimp you've been using, has nothing to do with this partial incipient case separation.
 
Slamfire said:
Since head space checked out ok then it's just case stretch from firing and full length re-sizing more than a few times. For my bolt action .300 Win. Mag. I neck size only and get several reloads from cases. I don't think I've tossed one yet due to incipient case head separation.

Full length re-sizing is recommended for lever actions.
Click to expand...

This. Saves me typing on my phone.
 
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