Treblig,
There are two books that,to me,are a must read to better understand the Birmingham gun trade. The first is,not oddly enough,The Birmingham Gun Trade by David Williams and Notes Around The Gun Trade by Bernard Hinchley.
These books describe a corps of out workers that was the gun making industry. In fact the system extended into the factories where workers were paid by the piece,brought there own hand tools and were paid by what they produced whether inside the factory or not.