Colt Expanse Kaboom

[26 Inf]

I still don't think that it was an overpressure event.

I believe Ned C. is correct with his theory.

In terms of over pressure, aside from everything else that point to over pressure look at the 13th picture in the OP's second post. Regular pressure doesn't flow into the ejector pocket like that.

Everything you see indicates a massive spike of pressure with no place to go.

[rickgman]

I believe Ned C. is correct with his theory.

In terms of over pressure, aside from everything else that point to over pressure look at the 13th picture in the OP's second post. Regular pressure doesn't flow into the ejector pocket like that.

Everything you see indicates a massive spike of pressure with no place to go.

That is exactly what happens when there is a case head structural failure.

[Ned Christiansen]

The only case head structural failures I have seen have been, I believe, due to a high-pressure event. I have seen case separation further up, like 1/2 way up the length, but they did not cause anything more than the annoyance of the forward part of the case being left in the chamber.

If a case head were to fail for some reason not related to extreme pressure, a flaw in the brass, say, I do not see it causing the extreme pressure signs of case head brass being forced to flow into extractor and ejector cuts. For example let's drill a 1/16 hole perpendicular to and from the extractor groove's angled part, into the case interior, and fire it. No excess pressure will be generated but she's gonna blow.

[rickgman]

The only case head structural failures I have seen have been, I believe, due to a high-pressure event. I have seen case separation further up, like 1/2 way up the length, but they did not cause anything more than the annoyance of the forward part of the case being left in the chamber.

If a case head were to fail for some reason not related to extreme pressure, a flaw in the brass, say, I do not see it causing the extreme pressure signs of case head brass being forced to flow into extractor and ejector cuts. For example let's drill a 1/16 hole perpendicular to and from the extractor groove's angled part, into the case interior, and fire it. No excess pressure will be generated but she's gonna blow.

Ned, if there is a case head structural failure the combustion gases flow into the extractor recess in the bolt and the damage is pretty much identical to what is seen in this instance. Remember, we are dealing with over 50 kpsi gas pressure. That level of pressure also equates to extreme temperatures.

I already posted this information but it might be worth repeating: "Case head failure or structural failure of the case head is the more destructive event. In that case the bulkhead or web of the case cracks open, often through the primer pocket and exposes the bolt face, extractor, and ejector to hot plasma at peak chamber pressure. In the AR, the plasma jets out the back of the case, curls up the extractor, moves down into the bolt, and bolt carrier, and may cause these items to split. Sometimes there is sufficient volume of gas in the upper to cause further splitting of the aluminum receiver housing. Often the primer cup is vaporized and may be found redeposited as a brass plasma coating throughout the action. Usually the gas also jets into the mag well and blows remaining rounds and the mag floor plate out. Sometimes the mag and mag well are ballooned out by the pressure pulse. The remains of the bolt may be found locked or unlocked after the event in the barrel extension depending on whether or not sufficient plasma reached the "Piston" space between the bolt and bolt carrier, enough to drive the bolt carrier to the rear and unlock..

Case "separations" usually occur at the most brittle and thin portion of the case body. Mil Spec case temper profiles show that to be at a point that is inside the chamber so both circumferences of the separated body are within the chamber.

Case head structural failures occur in the unsupported portion of the case outside of the chamber, so there is no chance of sealing the gas at that rupture. There is no gas seal between the closed bolt head and chamber face, other than that offered by a properly functioning case structure."

[Ned Christiansen]

I will keep an open mind about that, and my eyes open for a test subject this summer-- I'd really like to try this with a "manufactured" case head flaw.

I stand by my theory though as to the cause in this instance given the difficulties in chambering rounds and the unburnt powder in the action.