rpharder, The S-16 barrel was introduced in 1989 in 22lr, 22mag, .223Rem, 7 x 30Waters, .30/30win, 35Rem, .44mag, 45-70, and 45Colt/.410. Like the 21" carbine barrel introduced several years before, it had one screw boss for the forend. According to the illustrations in the catalogs, both the 21" and 16" went to two screws in 1992. GOOD SHOOTIN', Walt