This one is a Crescent Arms Model O. It might actually have 2 ½-inch chambers; a lot of these guns did. “American Gun Company” was a name used by Crescent Arms of Norwich, Conn., on its trade brand name guns, which were produced for many different retailers (as in somewhere from 175 to 450 depending on which expert you believe) under many names from 1888 to 1931. Crescent would produce orders for as few as 12 guns, apparently, if the customer would pay for a die to have its business name stamped on the receiver. Otherwise, you could order guns marked “American Gun Company” until shortly after WWI, at which point they were stamped “Crescent Arms.” Unfortunately, Crescent’s records were a victim of the war effort, having been donated to a paper drive sometime during World War II.