[John Sabato]

Originally Posted by sheepherder

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.