"Incredibly complex" is not how I would describe a double shotgun action. Even the most sophisticated self opener, the Beesley action, is fairly simple compared to other mechanical apparatus, like a watch, for instance.
Gunmakers have convinced their public that their product is complex to justify an upward spiralling price.
A Ferrari is incredibly complex, and goes for 150 USD a kilo, while a comparatively simple SXS best sidelock goes for 50 000 USD per kilo.
Fogings were beyond the scope of gunmakers, requiring heavy machiney and an industrial location. Some machining was done in house. Greener mentions and advocates the use of machine tools.
In later years the machining was outsourced and some firms made a name as the suppliers of machined actions to the "trade". I think the most famous of them were Philipsons. Speaking from personal experience I saw cast Dickson receives displayed by a Dutch investment casting firm in a defence exhibit. The same firm, if I recall, had castings of the Greener GP receiver.
The arrival of CNC machines, which are enclosed, therefoe quieter and cleaner, have brought machining back in house.
