I had a partial case head separation using a 1.8oz buffer

[DeNinny]

Peak pressure happens directly in the middle of the propellant column, per Aberdeen and every other major company that has placed piezoelectric gauges over chambers and measured the variances.

I don't dispute this. But it is irrelevant to my failure models. What I need to see is this type of data during an actual failure. One similar to OPs would be great. What you are sharing is what happens under normal conditions. That curve will be much different for an in battery case rupture. At the beginning it would look fine. T = 0. And for sure any in-battery case rupture is going to occur between T = 0 and T at peak. And if it happens before T at peak, then it will immediately drop below that point after that.

In-battery case failures happen due to peak pressure finding a failure node in the brass or an incorrectly-cut chamber.

Agreed. The failure node in the brass was at the bend point as it bent to the shape of the feed cone. This was at the extractor location too, where the brass had literally more volume to expand into.

That failure event is extremely close to ignition, which means you now have substantial pressures venting into areas of the system they shouldn’t be.

To be clear, there are two areas only. The rupture point and the mouth of the case. The gas will escape only those two points and the one that happened first will have more gas escape that way.

When this happens, you see massive and irreparable damage to components like in the images I posted. You don’t have clean egress of the escaping high pressure gases without noticeable damage to the upper and nearby parts, with a few exceptions:

When this happens the damage will depend on the pressure that causes the failure like I already explained. You are again assuming the amount of damage dictates one particular failure. That's an assumption but it's possible to just have a blowout in battery with only enough residual pressure to blow out the magazine. Again, each failure case needs to be analyzed individually. there will be similarities AND differences in all of them.

In a partial case head separation, the vast majority of the pressure has already subsided because the projectile passed the gas port already, but there is more than enough bore pressure to push brass around:

...

Imagine a 6.5 Grendel pmax of 47,000-50,000psi, taking propellant volume (more than 5.56) into consideration, as well as bore volume, then overlay it on this same type of graph.

You can see that CLGS port pressure could easily be 20,000psi or higher at that port location.

Now look at the pressures between the port location and the muzzle.

This is the plug dwell time.

See how there is enough pressure still being exerted on the case (temporary gasket sealing the rear end of the vessel) so that if the case moves rearward even just enough, the brass can yield since it’s no longer being supported?

This is true regardless of the cartridge.

Edit: I misunderstood this the first time. I'll simply say again that the brass was already not supported. There doesn't even need to be a reason it shifted. The existing unsupported and weakened spot ruptured at a high "enough" pressure. No shift needed.

If there was significant axial force being exerted by the extractor in a certain clock location, stressing the brass in that place, that location is more likely to initiate the failure node from a combination of axial strain and internal pressure.

This is exactly what I think we are seeing right here:



And because I was spending so much time discussing the fleet performance of Lapua brass, I totally missed this other critical detail:

All this is simply explained by an in-battery case head that is ballooning into the unsupported area of the feed cone and also into the area of the extractor due to the smaller volume of the extractor relative to the lugs.

That's exactly what I see. Again. And goodnight for now!