What causes this brass-stripping off case head?

[gunsandgunsmithing]

The primers in your pictures didn't support the overpressure theory.
I don't understand the argument that ejector swipes are indicative of overpressure to begin with.
Extractor marks/gouging- absolutely. High pressure makes the case difficult to extract.

The ejector does nothing to the case until primary extraction has already occurred.
It is the naturally occurring motion of the ejector pin to swipe across the casehead as the brass clears the receiver cutout and can be pushed outward. I've got an AR in 6.5 that routinely needs brass shavings cleared from the boltface due to a very stiff ejector spring; I suppose I could disassemble the bolt, take a couple turns off the spring but I just don't consider it anything that needs to be "fixed".

Someone explain to me how swipe marks from an ejector are related to excessive pressure?

Because the brass flowing into the hole creates the high spot that gets sheared off by the edges of the ejector hole when the bolt is rotated. It's not the pin but the hole.
Edit...yes, softer brass in the area of the case head is a contributing factor. Norma is notorious for this.

 

[KY_Windage]

I pretty much eliminated pressure as a culprit when I realized it was happening before the cartridge was fired. It was also doing the same thing to Hornady brass.

The Norma does seem a little soft, however. I just ordered a couple of smaller expander mandrils because my neck tension seems a little light with my standard .263 mandril.

BUT, I'm not certain that brass is softer. The Normas also have wonderfully even, but thin, neck-walls.

 

[powderbrake]

Someone explain to me how swipe marks from an ejector are related to excessive pressure?

It is the ejector hole, not the pin. It occurs as you open the bolt, the case is "restrained" by the friction of the case to chamber, excess pressure can cause the brass to flow into the ejector hole. The sharp corner on the hole can shave off some brass.

Sometimes with high pressures the case extrudes down into the hole, and it easy to see on the case after extraction.

 

[gunsandgunsmithing]

As others have alluded to previously, another contributing factor can be headspace. I have lapua brass that will show ejector swipe(yes, it has a name) on the first firing but not on the next, same load and speeds, from a top of the line custom action.(multiple).

Here's a pic of a piece that has multiple firings of the same load, from the same gun, for example. Notice only one swipe mark and while the load is stout, the primer is still not terribly flattened.

 

[tobnpr]

excess pressure can cause the brass to flow into the ejector hole.

Never heard of that before.
You're saying that the extremely thick brass at the bottom of the casehead- the thickest section- will "flow" like a primer does into the clearance around a firing pin? I'm skeptical.
Primer cups are very thin and soft, that brass surrounding them is thicker by orders of magnitude.

 

[gunsandgunsmithing]

Never heard of that before.
You're saying that the extremely thick brass at the bottom of the casehead- the thickest section- will "flow" like a primer does into the clearance around a firing pin? I'm skeptical.
Primer cups are very thin and soft, that brass surrounding them is thicker by orders of magnitude.

That's exactly what it does do.
Here's an EXTREME example!!
The case failed at the ejector hole. It was a ppc case head od, on a .308 bolt face...and, drum roll...a sako extractor!
You can clearly see where the brass flowed into the extractor cut but that's not where it failed.

 

[Jesswil61]

Hodgdon says for 1:9 24" bbl (mine is 1:9 26"), 130-gr and H4350, the recommended start is 39.7 gr. and max is 42.7 gr. I am shooting 42.0.

Cases will go back in w/o resistance to closing.

It is even doing the swipe on deprimed, tumbled brass.

All the above lead me to believe it is not pressure related.

It has got to be the ejector hole rim, right?

If the cases will go back in with no resistance on close you could possibly back off your should bump some as well and limit some of the hammering on the bolt face.

 

[Jesswil61]

That's exactly what it does do.
Here's an EXTREME example!!
The case failed at the ejector hole. It was a ppc case head od, on a .308 bolt face...and, drum roll...a sako extractor!
You can clearly see where the brass flowed into the extractor cut but that's not where it failed.

If you are flowing the brass of a case head you have bigger problems ahead, the brass in a standard chamber may flow approximately 2/3 of the case length, more than that you are pushing an edge that will eventually cause a catastrophic event! Typically the tell tell signs going on on a case head is caused by too much head space from bumping brass to far or a long or large diameter chamber. Pitted bolt faces, or protruding rough surfaces as determined here are the other culprit.

 

[gunsandgunsmithing]

If you are flowing the brass of a case head you have bigger problems ahead, the brass in a standard chamber may flow approximately 2/3 of the case length, more than that you are pushing an edge that will eventually cause a catastrophic event! Typically the tell tell signs going on on a case head is caused by too much head space from bumping brass to far or a long or large diameter chamber. Pitted bolt faces, or protruding rough surfaces as determined here are the other culprit.

The pics I posted in the comment you quoted, have nothing to do with any of that. They are a clear example of brass flowing in an extreme overpressure event.

Brass flowing into the ejector hole is EXACTLY the same, but at lower pressure than my extreme example quoted. My previous post is an example of a headspace issue along with a borderline hot load. Neither bolt was pitted or rough.

 

[243winxb]

If you are flowing the brass of a case head you have bigger problems ahead

Many newer factory cartridges run at 65,000 PSI. The brass flow into the ejector hole can be seen on the fired brass.
Yes, factory ammo has extra head clearance. The chamber may still be wet. This may cause flow with the extra bolt thrust.

The brass flow into the hole is getting almost to common

 

[243winxb]

From old Olin brass Co.- (now Wieland)
"modulus of elasticity- Cartridge Brass-
Material is 70 copper/30 zinc with trace amounts of lead & iron , called C26000. Material starts to yield at 15,000 PSI when soft (annealed), and 63,000 PSI when hard.
Material yields, but continues to get stronger up to 47,000 PSI when soft, and 76,000 PSI when work hardened"

 

[tobnpr]

So...why this "brass flowing into the ejector hole" still makes no sense to me.
The entire casehead is unsupported by the chamber. If there's enough "pressure" to force the brass at the base to "flow" into a few thousandths clearance- when it's otherwise FULLY supported by the boltface- explain how the entire 360 degree perimeter of the casehead doesn't simply fail with a catastrophic separation? It has ZERO support behind it.

In the case of Sako extractor related failures, that's a casehead failure that takes out the extractor. Hot gases and 60KPSI gotta go somewhere- I see no relation to this condition. Primers aren't even flattened- I reject that "overpressure" even exists here to any significant extent. Brass is soft as shiznit- a hard steel pin (probably with sharp edge) swiping across it will shave it. I'd bet that if the OP pulls the bolt, lightly rounds the edges on the ejector- and maybe- takes a couple turns off the ejector spring if there's excessive force needed to compress it, the problem disappears.

JMO.

 

[mikecr]

So...why this "brass flowing into the ejector hole" still makes no sense to me.

It is hard to picture happening, but it does. And as mentioned earlier, you can count on primer pockets loosening soon -because the case head IS expanding.


I stopped using Norma a long time ago because of loosening pockets.
This, while I could make brown box Lapua and Winchester brass last forever.

 

[liljoe]

Here is another extreme picture of brass flow into the ejector hole.
Joe

 

[gunsandgunsmithing]

So...why this "brass flowing into the ejector hole" still makes no sense to me.
The entire casehead is unsupported by the chamber. If there's enough "pressure" to force the brass at the base to "flow" into a few thousandths clearance- when it's otherwise FULLY supported by the boltface- explain how the entire 360 degree perimeter of the casehead doesn't simply fail with a catastrophic separation? It has ZERO support behind it.

In the case of Sako extractor related failures, that's a casehead failure that takes out the extractor. Hot gases and 60KPSI gotta go somewhere- I see no relation to this condition. Primers aren't even flattened- I reject that "overpressure" even exists here to any significant extent. Brass is soft as shiznit- a hard steel pin (probably with sharp edge) swiping across it will shave it. I'd bet that if the OP pulls the bolt, lightly rounds the edges on the ejector- and maybe- takes a couple turns off the ejector spring if there's excessive force needed to compress it, the problem disappears.

JMO.

Well, I respectfully disagree with pretty much all you just said. But, let me ask you this, because it might add some degree of clarity....Most bolts, in bolt action rifles rotate 90 degrees. Hopefully we can agree on this generalization. If so, then why doesn't the ejector mark go 90 degrees around the case head? Instead, the mark is a nice round hole at the ejector hole.

Another thing...if it were created by the spring loaded ejector pin, can we agree that would be a (scratch) removal of material from the case head, yielding a net depression in the case rim thickness?

I'm very familiar with these Mark's in several custom actions. I can promise you that it is in FACT not a depression in the rim thickness. Never, not ever, not a single time. Its apparent that some aren't familiar with this happening, but several have said exactly what I'm telling you and the OP.

It's ok to disagree about things that are opinion based but to disagree with what is known fact by several posters is just refusing to admit that you might be wrong about something that you clearly arent familiar with, but are merely theorizing against what most of us know is not at all theory.

Good night my friend. I dont wish to argue this further.

 

[Alex Wheeler]

Brass does flow into the ejector hole. Under enough pressure it becomes plastic. The case head does also expand but not nearly as much because the forces are different. The pressure inside the case acts in all directions, but the pressure forcing the case head outwards has less surface area to act on that the pressure forcing it rearwards. Ejector marks are a pressure sign, and even if the brass is soft and your pressures are safe, its still telling you that brass cant handle that pressure.