Pretty nice work on the carving. The initials on the thumbpiece inlay usually indicates the initials of the first owner of the rifle. Its likely this rifle was made by the maker for himself. If he had made it for a customer, the maker's name and/or initials would be on the top or left of top flat of the barrel. Being in the business of crafting rifles, he would have either stamped or engraved his name as the maker.
A muzzleloading firearm, rifle, fowler, or pistol with the maker's name affixed becomes his "business card". He would want to sign his work. Occasionally, the maker might sign his name on the bottom of the barrel, especially if the customer were furnishing the parts instead of the maker.
