RE: How does a laser bore site work?
laser boresighters work well, but I agree that looking through the barrrel works as well, especially if you have a big caliber (30). I use the laser at home when I do some maintenance on my rifles.
I start with a rifle that is already zeroed and aim across the basement at a sighting target. I mark the position of the laser bean on the target when aiming dead center. Now you can remove your scope, put it back and recreate the same alignment. Your rifle will be zeroed.
If your scope is mounted 2.5" above the bore axis the crosshair will be approximately 2.5" higher than the laser mark.
You have to remember the laser are not perfect and they might shoot at a very tiny angle from the axis of the barrel.