My 17-6 has the 4" lugless, heavy barrel, that Camster alluded to. In poor light, its ramped front sight is harder for me to see distinctly, but in good light the 4" tube is extremely accurate.....I remember someone saying in a discussion on this forum that the 17-6 resulted when S&W dropped the M-18 and installed left-over 4" barrels on M-17 frames. Don't know if that is true or not.