These caliber specific arbors accept the Aimshot Bore Sight. Simply insert the module into the arbor and then insert the arbor into the chamber. A bright laser beam shines through the bore of the gun and is visible on the target, allowing for initial sighting in of optical sights. This system saves time and money that would otherwise be wasted getting the shots "on paper." For 7mm Rem. Ultra Magnum, 300 Rem. Short Action Ultra Magnum.