A person could very easily mark the edges of the laser cartridge, and then rotate it in the breech while recording the eight places it hit the cardboard.
Draw lines between each of the opposing eight spots and where the lines cross is the centerline of the bore.
Do both barrels.
Once you mark your spots, you can figure out how old the two barrels shoot relative to each other.
Lateral dispersion or convergence is one thing, but if there is a substantive difference in elevation, and the breach was level, you have a real regulation problem.
