Well, had this happen today...

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I would worry more about the diameter of the chamber at the base than the headspace. If the chamber were the right diameter I can't see how it would have extracted easily with that big of a crack... I could see it extracting easily if the chamber were over sized. I would check the chamber dimensions before I shot it again not just the head spacing.
 
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Could of been load a little too hot by accident. And you discover it when you fired it.

Probably not. I’d expect an overcharged round to blow out where the case is unsupported by the bolt face, this one didn’t. The easiest explanation is that there was a flaw in the case from when it was drawn and the case blew out there.

If the chamber was oversized enough to get the case to blow out I should be consistently blowing cases. I’ve had two failures out of about 400 rounds from this lot, so I’m thinking it’s unlikely.

BSW
 
Update after the Saturday rifle match and about 150 rounds fired: Everything was normal, rifle worked perfectly with no problems.

Prior to the match I did check headspace and the bolt doesn’t close on a field gauge. The lot of ammo I shot this weekend is PPU from 1983. The bad lot was IK factory from 1976.

BSW
 
My vote=bad case. Over pressure or excess headspace would flatten primer.

Regards,
hps
 
Right through the thickest part of the brass...ouch. Good thing the vz-58 is one seriously overbuilt tank. You won't have any damage. Definitely pull the bullets and destroy the rest.
 
Yugo M67 with 1976 headstamp, fired from vz58. Got a face full of smoke but no debris. Rifle looks ok and I'll check headspace before I shoot it again.

I had another case separation last summer from the same lot, also in the vz58. Needless to say I won't be shooting anymore of that lot.

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BSW

Briansmithwins: I would like to use your pictures in my continuing saga to educate the shooting society that gunpowder has a indeterminate but finite shelf life. Do not confuse indeterminate with infinite. Indeterminate means unknowable. Gunpowder not only has a finite shelf life, but as it ages, it gets worse.

But, your ammunition is 43 years old. That is old stuff. One of those rounds will have burn rate instability and is going to blow up the firearm it is fired in. Happens all the time, and shooters attribute the blow ups to anything but old gunpowder.

I have written extensively on the problems of old ammunition:

Enfield extraction problems

https://www.thehighroad.org/index.php?threads/enfield-extraction-problems.853036/#post-11165247

Old Ammo

https://www.thehighroad.org/index.php?threads/old-ammo.842597/page-2#post-10948598

Oldest Ammunition you'd carry

https://www.thehighroad.org/index.php?threads/oldest-ammo-youd-carry.830197/page-3#post-10721487

Ammo storage

https://www.thehighroad.org/index.php?threads/ammo-storage.826681/#post-10655

All the shooting community wants to hear is that they are going to be around forever and their hoard of old ammunition will be perfect till the end of time. However, I will say, the most likely cause of your brass failure is corrosion due to NOx outgassing from old, deteriorated gunpowder. NO2 is one byproduct of NOx and it is an aggressive oxidizer. So, NOx created internal corrosion and the case head split.

For anyone who experiences similar, I would stop shooting that ammunition. A smart thing to do is pull the bullets from all cases, and examine the cases for signs of internal corrosion. The bullets are absolutely reusable, there is risk with using cases that come from a known lot of old ammunition, even if you can't see corrosion inside. Dump the powder and always wear your shooting glasses.
 
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I have seen separations with x 39 from AK's, RPD's, RPK's, etc. using surplus euro and chinese ammo- always just forward of the rim. Not uncommon, but not epidemic. Never seen one like that, though.
 
I have seen separations with x 39 from AK's, RPD's, RPK's, etc. using surplus euro and chinese ammo- always just forward of the rim. Not uncommon, but not epidemic. Never seen one like that, though.

Case head separations are a pretty good indication of excess headspace. Once your headspace has opened up that much the problem will continue until the headspace is corrected.

Since mine is a split through the rim that had hundreds of rounds between separations I’m going with the idea of a flaw in the case, perhaps made worse with by the age of the ammo.

BSW
 
Case head separations are a pretty good indication of excess headspace. Once your headspace has opened up that much the problem will continue until the headspace is corrected.

Since mine is a split through the rim that had hundreds of rounds between separations I’m going with the idea of a flaw in the case, perhaps made worse with by the age of the ammo.

BSW
In most cases I would agree with you, but I have seen this happen with fairly new AK's in good condition. The x factor was generally the ammo. That being said, ammo was generally on the old side, and not stored under optimum conditions (war zones in the mideast).
 
Never saw one that far back but do know of some that cracked or split side. It was old ammo that was not stored well and was actually so old it just shouldn't have been sold. Even salvage was pointless since the bullet was the only part salvagable. The guys bought it at a gun show. Some wouldn't go off, not even squib. Some were low pressure. They went straight back to gun show and showed the people runing it and the police. They made them stop selling it.
 
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