That tool from Woodcraft Supply looks fun, but a set of proportional dividers from Ebay will prove more useful.
Not only will it adjust to a 3:5 ratio, but it can do 5:8 (closer to the Golden Ratio) and a long list of other proportions. It can function much like the sector mentioned earlier. According to the instructional booklet that came with mine, this tool is way smarter than I am.
By the way, proportional dividers are illustrated in Wkyke's catalog of watch and clockmaker tools published in England in the mid 18th c.
Without wanting to diminish the importance of the Golden Ratio and the scholarship that has surrounded it, it is but one proportional system among others. Emphasis on it has over shadowed another approach that was central to an 18th c. design education: understanding the orders of Greek architecture.
These orders were a modular systems based on even multiples or simple divisions of some base unit. Chippendale's Director devotes the opening chapters to the correct execution of these orders as a foundation for furniture design. I have also seen 18th design books for architectural ironwork in which gates and screens were explicitly described as done in the "Ionick" taste etc.
Of course, as the ultimate arbiter of what looks right is the human eye, there is bound to be an overlap in proportional approaches to design, or even multiple approaches used depending on the context. In period style ironwork, for example, it often seems like the overall design falls into various expressions of the Golden Ratio, but details express simple multiples of the dimensions of some basic motif.
Did 18th c. American gunsmiths explicitly apply these approaches to guide their design decisions? I don't know. If they did, they didn't seem inclined to write about that or much else beyond the business aspects of their work. On the other hand, other tradesmen in Europe and England did explicitly write about such things. It's hard to imagine that formally trained gunstockers like Albrecht would have been ignorant of formal design principles. How much of that knowledge might have been retained and passed on as the longrifle evolved is a fascinating question.
