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

[LRRPF52]

To me you are claiming the effect is the cause here. "Peak" pressure is completely over as soon as either 1) the bullet leaves the mouth or 2) the blowout occurs.

The blowout occurred because pressure was at some level inside the casing and it simply reached the necessary force to rupture the brass. This is MY definition of "peak" pressure. The laws of chemistry and materials science dictate this.

The reason a metal deforms is because force (or pressure) is applied to it. And all materials, metals/alloys in particular, go through a phase of temporary deformation. And then if enough force is continually applied, the metal will reach a point of permanent deformation. At this point, it will never restore itself to original shape. And then if even more force is applied, the metal eventually ruptures. And then once that rupture occurs, the metal wall itself is no longer holding back all that pressure so it immediately dissipates. The pressure will not ever "peak" after this.

And in this failure, as soon as that rupture occurred, at whatever peak pressure it took, the pressure dropped. This is how the pressure will respond in any fully pressurized vessel that is pushed to the point that a weak point permanently deformed.

So with all this, the pressure was not "residual" as you stated. The pressure was rising with the cartridge in battery, it simply reached the point of stretching the brass into the feed cone, at which point it started permanently bending to the shape of the feed cone. And then finally, the force (pressure) reached the point of tearing it. And since a bend is a weak point in the alloy, the tear started there. This is all from the pressure within the case that started building as soon as the primer fired. And it kept building until the brass ruptured.

And remember, immediately after the tear started, pressure started dropping rapidly. Plus again, the bullet leaving the mouth dropped it a lot too. So there definitely didn't need to be all this other extra pressure to do all that damage as you are assuming would happen.

The pictures are evidence that the brass ruptured in battery as per all my other points. Above is the chemistry and material science theory of how it happened and is all 100% consistent with what I see in the pictures. Every blowout will happen the same, and yet the peak pressure at which it happened doesn't have to be exactly the same.

To me you are assuming all blowouts have to have nearly the same damage. The science to me says otherwise. You have to analyze each scenario in depth to flush out those differences.


Agreement!!!


Not necessarily per all my points above.



To me these are all just higher pressure failures. The OP's failure just happened at a lower pressure which still happened in battery. Clearly and lucky for him!


This is exactly what the pictures support and as I have described. IMHO.

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.

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

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.

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:

Exotic alloy bolts, barrel extensions, and beefy billet uppers.

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.

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:

Actually - it's a full Odin BCG and bolt - here's the exact item I purchased:

https://www.joeboboutfitters.com/Odin-Wo...tg-bcg.htm

One other interesting bit about the pistol is I put a Strike Industries short pistol buffer tube with a 1.8oz buffer on it:
https://www.strikeindustries.com/si-ar-spre-slick.html

Would a light buffer potentially put extra strain on the case a bit early? It's a carbine gas system.