They're awesome photos, thanks for posting them.
The English proofs on the barrel flats appear to be from between 1904 and 1925.
The gun appears to actually have been built by Lancaster in England, and as Huvius has noted on the other forum, the action is of the assisted opening type. This system can also be found on other Lancaster guns. It was originally a Beesley design.
It's a nice double and chambered for a very highly regarded cartridge, the 450 NE No2.