Norc M14 case separation - photos included

[Z06corvette]

So I was at the Olds range today shooting my 2007 Norinco M14 when the third round chambered went click but no kaboom (good thing). I stroked the bolt thinking maybe I had a bad primer, but the next round did the same thing. I looked into the breech to see that the round had not fully chambered (makes me nervous that it would drop pin out of battery) so I cleared the rifle and then noticed that the second round ejected during firing had separated at the shoulder, and the shoulder and neck were still in the chamber.

I examined the cases and discovered that the primers of the two rounds fired were pushed out slightly and there was cratering around the pin strike.

The ammo is American Eagle 150g FMJ, on a previous occasion I had fired 20 rounds of the same ammo through it with no incident, although I don't remember if the primers showed the same issues. I had fired the two rounds across the chrony and they were about 2835 fps.

Is this caused by excessive headspace? I was going to send 3 cases to Hungry for checking but this happened first.

I would appreciate any help on this.

Gord.

 

[M14Doctor]

I've had this happen once, same ammo as you are mentioning and eventually ruled the cause as crappy brass.... not saying this is the case here but it was my experience with the american eagle ammo. the rifle was a nato spec chamber well within the safety zone for headspace. Another culprit can be an excessively dirty or fouled chamber.

 

[Z06corvette]

Hey Doc, what are you doing up so late?

I will load a few rounds in some Winchester brass and see what happens... as long as they hold together I'll send them to Barney for measurement. The chamber is clean, when I bought it new I completely stripped the rifle down and cleaned dilligently, only about 20 rounds since then.

Thanks for your response.
Gord.

 

[BattleRife]

That is the most bizarre failure I've ever seen. Headspace failures do not occur that high up and manufacturing defects are almost always longitudinal owing to the way in which cartridge cases are deep drawn.

Will you send me that case? I will put it under the microscope and at least tell you the mechanics of the failure, and maybe we'll be able to put our fingers on the root cause.

 

[Claven2]

Headspace failures occur back by the base of the casing. that failure is because the brass was not ductile (too brittle from too much work hardening during manufacture).

I would guess Federal does not anneal their cases. (those are Fderal cases 100% for sure - I know the headstamp)

Try another brand of ammo and the issue should go away.

 

[BattleRife]

All manufacturers anneal their cases, if they did not a significant percentage would crack before they were even removed from the box. Additionally, firing a cartridge in a normal chamber imposes predominately hoop stresses on the case, resulting in longitudinal splits in a homogenous material, not circumferential ones. And finally, while the photo is not close enough to tell with certainty, the wavy edges of the fracture suggest a shear lip, which results from ductile failure.

Portions of your conclusion may well be correct, but neither you nor anyone else can tell from that one photo.

 

[Z06corvette]

That is the most bizarre failure I've ever seen. Headspace failures do not occur that high up and manufacturing defects are almost always longitudinal owing to the way in which cartridge cases are deep drawn.

Will you send me that case? I will put it under the microscope and at least tell you the mechanics of the failure, and maybe we'll be able to put our fingers on the root cause.

PM sent.
Thanks.

 

[M14Doctor]

All manufacturers anneal their cases, if they did not a significant percentage would crack before they were even removed from the box. Additionally, firing a cartridge in a normal chamber imposes predominately hoop stresses on the case, resulting in longitudinal splits in a homogenous material, not circumferential ones. And finally, while the photo is not close enough to tell with certainty, the wavy edges of the fracture suggest a shear lip, which results from ductile failure.

Portions of your conclusion may well be correct, but neither you nor anyone else can tell from that one photo.

man, that's cool...... there's some science goin on here.
i'd love to hear ... or read rather, the results and conclusions you draw from microscoping that case
thinking back over the years.... I had an sks, those "sporter" ones that came in the mid 90's with fat stock and rubber buttpad....... the first shot i fired from that gun did this exact same thing..... and it stayed in the trunk for the weekend till i went home and got a broken case extractor. american eagle x39 , red box.....
then again in an m14s and both times i could not really say for sure what the problem was, but i never bought american eagle FMJ again.
I shoot piles.... mountains of federal premium ammunition,mostly soft points.... and the brass is excellent, never an issue.

ya know what..... that case from my m14s ..... it's here somewhere in one of my bins..... i'll dig it up and take some photos if i can