Your rifle is original, including stock, barrel and hardware. It's hard to date it without seeing how thin the butt is, and the box style, if original, would appear to be a later box probably from the percussion era...despite having the original flint lock in the gun. After seeing the lock bolt washer, cheek inlay and wrist inlay, they have no engraving, but there are three small punch marks on either side of the lock bolt head, which are somewhat similar to the punch marks used to decorate around the screw heads in the patchbox...so maybe the gunsmith never learned how to engrave, and did punched decoration to "kind of" look like engraved designs.
The large tab on the butt end of the box lid still looks odd, but the cavity inside the box looks good, so the box is probably original to the rifle. I still can't tell if the screws attaching the patchbox have modern machine cut slots with parallel sides/walls and a flat bottom, or if they are old screw heads with a "V" shaped slot from being formed by a chisel cut. I would have thought, from the patchbox and general appearance of the rifle, that it was a ca. 1840 percussion gun. But the original flintlock in the gun looks good, with good wood margins around it suggesting it may be original to the gun. Makes me think perhaps it's a percussion era rifle [as the butt curvature suggests] where the owner preferred to have it made as a late flint gun for personal reasons....but the lock style looks like an older ca. 1815 lock was used on an 1835-1840 rifle. Kind of a "mixed up" rifle in some respects. Hopefully some others will have ideas about this rifle, or see something I've missed. Shelby Gallien