The Obsidian9 is optimized for 9mm for additional suppression while staying light and compact. Our ADAPT(TM) Module gives you 2 lengths in one suppressor, for maximum suppression or weight/length savings. With a diameter of 1.37\" the Obsidian9 is compatible with pistol suppressor sights, making it perfect for pistols or sub-guns. Obsidian9(TM) Caliber Ratings: Belt Fed Rated for Pistol Calibers up-to 9mm 300BLK Subsonic (with an 8 or longer barrel) 9x39 Subsonic (with an 8 or longer barrel) 350 Legend (with a 16 or longer barrel or longer)