Wool bore mops 17 cal rifle wool bore mop, pkg The natural spring of wool helps the mop conform easily to rifling grooves; the looped and twisted brass shank and coupling won t scratch the bore.. Wool, brass shank and coupling. Rifle/Pistol 3¼" (8.3cm) long, 8 32 thread except for .17 cal. Advise cal favorite for gun cleaning; virgin wool mop holds lots of bore cleaner or oil, so both ends of the barrel get thoroughly coated. A classic wool bore mops 4dz/more r/p wool bore mop. Shotgun 2 7⁄8" (7.3cm) long, 5⁄16" 27 thread..