Again, I would agree with my fellow Forumites!
I'd place it mid to late 18th due to the 'cap' type guard that would fit over the scabbard throat to prevent rain water drainage into the sheath (and thus a risk for rusting). I've never seen this affectation on (later) 19th century pieces and it was sort of an 18th c. thing. Beautiful example, 'Nando and I like the honey patina of the grips!