A small update.
An interesting design feature that I hadn't noticed before became obvious at the range last week. After firing some 25 shots, I had a failure to extract the last round. Nothing curious, as it can happen. When I put down the gun, I noticed somethig odd: The barrel insert was missing. Had another look and saw that the chamber side of the insert was still there.
Puzzled, I started my search down the indoor range and found that the barrel insert had launched itself from the barrel, landing some 5 yards further.
The barrel insert is actually not a 1-piece deal, but rather a separate barrel that has been press fitted into the chamber part. I included a detail scan of an Erma drawing of the set. The red part is the barrel, the yellow part is the one-piece chamber insert.
It seems that, for some reason, the insert had worked it's way loose and the pressure of the last round was enough to launch both the round and the barrel insert forwards (the round exited the barrel insert normally).
I think that this design feature really isn't such a good idea. I pressed the barrel back into place and will do some further testing to see if it works loose again. It should be easy to find a way to fixate the barrel to the chamber part, and I wonder why Erma cut corners here?
Or perhaps the barrel insert will work it's way out every 75 years
