Ken,
Thanks for separating this -- it seems to come up all the time. Interestingly, the Bogle rifle (which is early) has pins fore and aft, with what must be a very long lug in the rear -- it appears to be pinned almost halfway up the wrist; just mentioning it as an example people might have access to look at in pictures. 1800 was a guess, but your fact about screw-making machine would help lend it credence as a rough guide. I also wonder if you think the predominance of set triggers on Southern rifles, which seem to me to weaken the wrist area compared to a simple trigger isn't another reason favoring a screw in the rear of the TG?