Back-action locks were in use well before 1860; I have a high grade rifle from Kentucky with a back-action lock that is dated in the signature "1837." In my experience, the early back-action locks were often stocked with a small side facing in front of lock, on both the lock side and on the reverse. The small side-facing disappeared within a few years, leaving the back-action gun smooth ahead of the lock on both the front and back sides, as yours is. Your inlays and box are not engraved from what I can see. I would date your back-action rifle to the late 1840s, maybe into the early 1850s. It's guard doesn't look later than that to me.The gun has a lot going for it with the forestock inlays, box, etc., plus decent bore size. It would be nice to see larger photos of the rifle, the more "standard" half-shot views of each side from the butt out to about 10 inches past lock plate, to get a better feel for the overall gun. All the small photos are good for details, but not to get a good idea of the whole rifle. Shelby Gallien