It's a beautiful piece. However, I'm a bit torn as to how to date it. I do not think it's a 1740s gun. Off hand I would put it maybe 1760s give or take a bit. What I find especially interesting is the three lock screws, especially because it appears the side plate was made to accommodate a 3rd screw, unless I am viewing the picture incorrectly. This would be extremely archaic even in the 1740s. The only explanation I can see for this, especially with a lock only 6" long, is that either the maker or the customer, or both, were outrageously conservative. Frankly despite the extremely artistry and fine construction of the piece, the three screw lock seems quite out of place. Also the third bolt seems to cut into the engraving on the lock in a way which leads me to think it was an afterthought, although if I am viewing the pictures correctly and the side plate is designed to accommodate the third bolt, might lead to contradictory interpretation!
Thanks for the photos because it's an awesome fowler regardless.