Ultimate Arms Gear .40 S&W & 10mm Caliber Internal Interbore Pistol Revolver Handgun Chamber Barrel Bore Borelock Muzzle Security Safety Key Lock for 10mm, .40 S&W Smith and Wesson Fits 3 1/4 " - 4 3/4" Revolver Barrel Length & 4 1/4" - 5 3/4" Auto Pistol Barrel Length