BELT GUN Second Shot or Second Guess

Bill shows his newly aquired belt pistol. Single shot caplock of unknown origin. Interesting lock design, swamped barrel, 60 caliber. The pistol has a cap box in the buttstock with an ornate lid. He asks if his audiene may know the origin of this pistol. Pistols like this are commonly manufacured in "Braces" or pairs. Bill likes to have a pistol as a back-up shot when traveling on his mule in the back country. Short grooves in the muzzle end are not rifling. What is the purpose of the grooves? Bill asks for the comment section to be used to discuss this pistol. Is it Spanish? Is it Turkish or English or something else?