How to keep particle beams fixed to their source and target points

I am trying to fix a particle beam to two points in order to make a laser pointer for VR, but the laser won’t stay completely fixed to the two points I am fixing it to on every tick.

This video shows my issue: https://drive.google.com/open?id=19kaXSNycBgdFrzPHHMiwIOQbYQbvkc30