Things You'll Need
Instructions
Empty a spent 12-gauge shell and a spent 20-gauge shell of primers. Use a small brush to loose the primer through the primer hole.
Slide the 12-gauge shell into the chamber of the shotgun and the 20-gauge shell into the muzzle.
Fix the barrel of the shotgun in a secure vise. It must be perfectly steady to properly bore sight the shotgun.
Look through the gun's scope and focus through the barrel. Line up the laser sight through the primer holes against a target.
Adjust the scope until the crosshairs are on the same area as the primer holes on the target.