Cleaning Rope Bore Blitz Cal. 50/12,7mm Niebling (9-50RF.21). The brass weight of theBoreBlitz is laser engraved with the calibre to make identification easy. Cleqaning ropeBoreBlitz 9-50RF.21 is a pull through cleaning device that cleans the barrel and chamber of Cal.50/12,7 mm firearm fast and effectively in shooting direction, without the need to disassemble the gun.