Interesting find, thanks for sharing
Looks like someone has tried to disemble it, takedown lever looks like it has taken a beating downwards and the sideplate looks out of place. Perhaps it the upper was placed out of battery at the same time..
I do not think it jammed this way during battle, it's not common for it to just get stuck in the rear posision without a case stuck at the chamber.
Perhaps you can post a photo of the extractor? It is found on top of the chamber and would indicate if there is a round inside the chamber or not.. The main spring is under tention.