I have never been a fan of the self-opening action as it causes to much wear and tear on the hook, knuckle, and hinge pin. I'm not sure if the gun described is a self-opener, but the description seems to imply that it was.

I believe the action described above was cocked by the weight of the barrels as they were opened and that is certainly the most efficient lever. The force of the self opening action supposedly cocked the hammers easier than relying fully on the hand opening the action.

It's hard to imagine another form of cocking mechanism being used as late as the 1930's, except for some of the odd American built guns (and there were some odd ones), other than the Anson & Deeley system, by any of the major makers.