I read somewhere, I don't remember where, that Dubbs was working somewhere in Bucks county as far back as 1755, I think...
There are no known signed Dubbs guns that I am aware of. The gun (and piece of a gun) that is in "The Kentucky Rifle: 1750-1850" (I think that's the proper title), and also in RCA is more than likely not by Dubbs. It has the initials "J.D." on the thumbpiece (which traditionally is the initials of the owner, not the gunsmith), so someone thought it "must" be by Jacob Dubbs. It is also "dated" 1721... :shake:
My thought is that these two guns (and another that has imported English hardware, as opposed to the German hardware on the two illustrated guns) are closer to 1790...
There are some guns signed "Jacob Daub", which is probably this maker, or his son. Late 18th/early 19th century. I'll look at my books and try and direct you to some photos of the Daub guns.