Earlier in the thread Daryl H made mention of "Espingarda Perfeyta" or in English "The Perfect Gun" which was 1st published in 1718.
This is the original cover. The book is written by 3 brothers who dedicate the work to King John 5th of Portugal.
Here is a plate from the book showing workman making barrels.
They describe at least 2 methods for making barrels. The first involves a twisting of metal of various gauges to form the barrel. They also describe the "Catalan" method of spiral wrapped barrels. Two men work on the same piece-the authors stress the negative effects on accuracy of working at this strenuous trade while tired-and the tools of the trade are scattered on the ground, as well as some partially finished section. Great care is emphasized to produce the strongest barrel possible to with stand very stout loads.
A couple of thoughts. 1st this is after the siege of Vienna. They make mention of procurring steel from various city states through out Europe. 2nd Portugal would have been a natural setting for this transition of technology from the Isalmic world.
Pete
