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

[LRRPF52]

I disagree because it could have easily dissipated. Remember that the pressure was also dissipating at the bullet end. And again, as soon as the blowout started. Pressure is going to drop like a rock.


Or, there was enough pressure to blow the case wall. And it started relieving there and also through it's normal path. With two escape routes, the mouth and the blowout, the pressure dissipated VERY quickly.


Earlier case failures (2) are supporting the failure model because their deformation shape and location of score line are indicative of the unsupported head area expanding to match that of the feed cone shape (to a degree). Unfortunately the third failure, the blowout one, expanded even further, to the point of blowing out.

Again, all the pictures are supporting this. To a "T". And the intact extractor is irrelevant here. It played no role in the model I'm explaining. And with the two cases NOT blowing out, of course it would stay intact!


I have seen them. This failure is just one that happened at a lower pressure than those others.

If the brass yields in-battery, it will happen more as a result of peak pressure, not residual pressure post-exit of the projectile.

The farther the projectile moves from the chamber, the lower the pressure is.

If the brass yields in-battery, you will see substantial damage to the action.

I would expect to see this with a case yielding in-battery:



When extractors appear to stay intact with an in-battery case failure, they look like this:



The existing structures outside of the barrel shank, tennon threaded into the extension, extension, and bolt are not designed to handle escaping gases of a 47,000psi or greater peak event.

They will direct the explosion away from the shooter’s face though, which is one of the nice features of the AR-15, as opposed to several other designs.

But what we have seen is not indicative of a case failure in-battery.