the self-opening function is real and can be traced to the ejectors, an unusual option.
They push against the breech face, thereby providing the opening function...
I am not sure if this was a feature or a by-product.
Anyways, not a bad gun, but not cheap indeed.
Note the lack of St-etienne proofs. It seems like la manu was at some point authorized to do their own proofing.
All the best,
WC-