Sorry but please be more specific as to what "mechanism". Locks ,ejectors lever work ?. No one held a patent on the idea of a side by side or an O/U as both have been around since the days of flint guns if not before .The side by side evolved ,different makes putting their own designs into production ,different lock types ,ejector work .etc but all essentially the same gun as most production cars are essentially the same [engine in the front ,a wheel in each corner and the steering wheel on one side ].British O/Us grew from trying to make a side by side turned through 90 degrees . Browning designed from scratch and got it right . Each maker looked at his competitors and either copied it or tried to re design it making most early British OU's in my opinion ugly ,heavy, over complicated and consequently troublesome .
