I've started digging long tunnels with the MG. Blazing fast! Just at some point the run-out of your looking vector from the horizontal level will make the laser go off from target and stray the 3x3 tunnel off the straight line.

Or as per the "autoaim" remark just make the look vector (or the resulting beam vector) "stick" to the cardinal direction vectors.

Could be an upgrade. This could also enable selected angles to be used, like 30°, 45°, 60° for example.