Interesting point about factory double charges. I was at my local Wal-Mart and I never really pay much attention to there recall board but it was near the restroom and I was waiting for a friend to come out and I glanced at the board and noticed there was a recall on Winchester 22 long rifle ammo due to a double charge so it does happen. To bad the one picture with the ammo near the top wasn't more clear with more of the ammo in it, if that is what the shooter was using. The back of the case looks fired and the primer possibly could tell us if the load was really hot. All in all I see the number 35 on a few parts and it would be a shame if it was numbers matching.

With both ears being separated, I wonder if it is a case not of excessive charge but of a missing/broken/ out-of-position locking bolt [takedown lever]. In that case, the only part holding the barrel extension together would be the axle pin, which very well might break the barrel extension at the ears.

This would also explain the relatively unbroken parts that a double charge would normally break.

Maybe...

Rich, the purpose of the locking bolt or takedown lever is simply to restrict forward movement, and keep the upper receiver in the frame while the gun is at rest, or at the completion of the firing cycle. There is no stress during the firing cycle, and in my opinion could not contribute to the failure that we see in these photos. The end toggle pin and the rear toggle link are what keeps the gun together during the rearmost movement of the gun during the firing cycle. IMHO All the stress on the upper receiver would be at the point where the forks have separated in the photos.

I would be interested in anyone else's differing point of view on the mechanics of this engineering... but I am pretty confident that I am correct in this presumption of how it functions.:rolleyes:

John,
for what it is worth, I believe you have analysed the forces correctly.

Take down latch would see no pressure at all in firing, only to stop the forward motion in counter recoil as you observe.

IMHO

Where the rear toggle link receiver ear intersects with the horizontal top of the receiver fork is a very sharp corner. Sharp corners can be points of high stress concentration.

The centerline of the receiver ear rear toggle pivot axle is slightly above the breech block centerline. This slight centerline difference introduce a bending moment into the receiver ear during recoiling of the breech block toggle assembly. The bending moment would be like tearing a sheet of paper as opposed to pulling it in tension.

As a police weapon and over almost a hundred years of use the receiver ear has been subjected to impact forces each time the Luger was fired. During this period apparently a crack was started at receiver ear-fork intersection.

Once the crack was started additional shooting would propagate the crack to ultimate failure.

That's my two cents.

Dick,
great description!
I haven't read of "turning moments" since physics class.:evilgrin:

It would be interesting to examine the broken parts to see if part of the crack line appeared to be older than the other part, like it had been cracked for some time prior to breakage. Not that it would really matter in the end...
dju

David, I think you are on the right track.

Cumulative cyclic fatigue is a phenomena that equipment designers should be concerned about. This phenomena was probably not considered when the Luger was developed.

I believe that an initial crack could be observed at the receiver ear-fork intersection. The pattern of material failure below the initial crack should be typical of tensile failure as the crack propagated.

Whatever the heat treatment for receivers was, the repeated pounding of use will tend to work-harden the material, making it more brittle. I agree with the idea of examining the mating surfaces of the break, which might give evidence as to whether a crack had been forming, long-term. Newly-snapped parts will be clean and sparkly over the face of the broken areas, and a crack that developed in the past, and finally let go, would show darkness/dullness/discoloration/oxidation in the extent of the ancient beginnings of the break. A good lesson to check these old girls out occasionally, under magnification--if not a session with leak-check and developer (harmless to the finish).