Abstract: An apparatus is provided for traversing a barrel of a gun and disposing at a select position therein. The apparatus includes a bore-rider assembly and a sight-mount assembly. The bore-rider assembly enters a muzzle of the barrel, slides within a bore of the barrel, and anchors to the select position. The sight-mount assembly projects a line-of-sight from the select position to the muzzle. The bore-rider assembly includes a rod having wedges, first and second bore-riders with proximal and distal ends, a sleeve couple that joins at axial ends the bore-riders in tandem from their proximal ends. Each bore-rider has a rim at the distal end and an extension at the proximal end. The rim has an outer diameter adjustable by expansion. The sleeve couple joins in tandem at each axial end each bore-rider from the proximal end. The rod passes through each bore-rider and the couple. The rod includes first and second wedges that engage their corresponding bore-riders.