I'm no expert ,not by a longshot and could very well be totally off base ,I'm just thinking out loud ...but that was no regular load or firing of a regular load ,that chamber metal would not have stretched like that , escaping gas is going to take the path of least resistance ,ie: a "cardboard" tube on a firework is loaded up with blackpowder ,but don't blow up ,it shoots out the open less resisted end ....a close examination of the case head if you have it may give a clue ...in my opinion the "crack " may have well saved you from more serious injury,it seems to have directed the blow upwards.

Very odd place for a crack too ?.

My guess is an obstruction,or overload .

I'm glad you escaped unscathed...sad about your gun though

The extractor guide pin hole is deffinately the thinnest point of the breech and a hard line may appear to be there because that may have need the start of what happened.

I do also agree that SOMETHING else happened here other than just pulling the trigger. The fact that everything blew out the back suggests that maybe the hull never opened up. Or maybe some sort of failure at the brass. Were the hulls used many times over?
It does not look like everything came out the front of the shell as it should have.

There is no damage or bulge at all in front of the chamber. And the blow out originated pretty much in the first inch of of the chamber.

Dr. Drew Haus is investigating a similar catastrophic failure over on the doublegundotcom forum. You should contact Dr. Drew if you're interested in what really happened.

The chamber wall thickness looks pretty stout - at least a 3-frame. That's a lot of metal to rupture through.
There appears to be quite a bit of rust under the top rib suggesting maybe a dip in water, or worse, saltwater at one time. The corrosion likely had some effect on the way it blew but my guess is some sort of obstruction. Remember in "Finding Out For Myself" it took 31,000 psi to finally destroy a Parker with composite barrels and I don't think that one blew out as severely as yours.

That is terribly unfortunate for the gun but I am glad that there were no significant injuries.

So if the metal was faulty, why did the stock also break? It doesn't add up. I suggest we get the CSI Miami team on it.

Wow! Look at those chamber walls and how they have been stretched. You say Gunter Pfrommer ID'd a crack in the chamber wall after the kaboom and it is still visable? I can't see it. Glad you are OK.

Like Dean said Dr Dreu Hause is investigating a very similar issue on another Damascus gun. Very similar.

Contact Dreu or atleast check out the double gun website.

I hope you were not hurt. I am sorry this happened to you.

Please keep us informed if you do figure out the cause.

Was the thought metal fatigue due to the crack, obstruction, over pressure/ over load?

David: I'm thankful you were not seriously injured.
As mentioned, right now METL here in Phoenix is finishing a formal failure analysis of a chamber blow out http://metl.com/services/
The 3 threads on DoubleGun
http://www.doublegunshop.com/forums/...=356377&page=1
http://www.doublegunshop.com/forums/...999#Post354999
http://www.doublegunshop.com/forums/...=357105&page=1

By the appearance of the blow out, I think there is little doubt that there was an obstruction, likely at the forcing cone, and would suggest that you examine every empty used prior to the event for a missing base wad or piece of plastic. AND please check the shell that was in the chamber for expansion of the head, and an indentation on the head from the extractor. Because of the plastic deformation of the chamber, I am quite confident that this was not simply a fracture of the barrel wall.

A formal failure analysis costs more than $1000, but if you would like to send me the remains, I could measure the wall thickness around the blow out and also ask the Metallurgical Engineer at METL for his opinion. Possibly a visual exam of the edges would confirm my thoughts.
Also please send the remnants of the shell, or post an image of the head.
Another option would be destructive testing of the remains, with sectioning and photomicrographs. This is the big $s.

BTW: I'll add your images here, with an attribution
http://www.picturetrail.com/sfx/album/view/24513874

Feel free to contact me at drewhausemd@yahoo.com if you'd like to discuss further testing.
Drew Hause M.D.

I wonder if these recent blowups have occurred due to detonation. Seems most if not all of these that were not the result of an obstruction were "lite" or reduced load reloads. Detonation occurs when there is too much space in the powder compartment and the powder burns instantaneously instead of progressively causing a huge pressure spike. It seems feasible that the wad in these reduced loads is not compressing the powder adequately?
Just a thought.