This rifle tells us quite a bit about late flint to early percussion gunmaking in Louisville, Kentucky. A. B. Semple began his long working career in Louisville in 1824, made both flint and percussion guns (rifles primarily) and later was involved in the hardware business as well as guns.
While we don't know for sure if this is a Semple rifle, it is strongly a Louisville rifle. The trigger guard with square corner above rear spur, double spurs, with the rear spur reversed, is very typical of Louisville guards in the late flint and early percussion era. Moses Dickson used virtually identical guards on his rifles of the same era. The oval "beaver tail" style cheekpiece is also typical of Louisville guns in the late flint to early percussion era. The architecture of the stock is close to that of Dickson's work as well, again cementing a Louisville origin. Further, note the lack of lower butt molding lines or forestock molding lines, another Louisville characteristic of this era, particularly on guns without patchboxes, which most lacked. Finally, while many KY makers used the more typical "two screw" type longer tang, in Louisville this pointed tail single bolt tang was more common, probably due to the heavy influence of river traffic that was a major customer of Louisville's gunmakers, and therefore had influence on the gun styles there. The long barrel, in a time period when other non-southern regions were shortening barrels, is again a KY and Louisville characteristic. It's unfortunate this gun lacks any part of an old signature, because if present, we could probably figure out who made it.
A good number of late flint guns made in KY (1830-1835) have single bolts on the locks, so it should not be a surprise to find one on a gun of this era, ca. 1830-1835.
I would think this gun might be an A. B. Semple rifle, and if not, then a Dickson. It definitely looks like a Louisville gun of the 1830-1835 era. While stocking is similar to that of Moses Dickson, the trigger shapes are different from those normally used by Dickson. However, if a Semple product, I would agree that the lock currently in the gun is not the original one. Semple didn't used the "& Brothers" after his name until at least a decade after this rifle was made. Shelby Gallien