RE: Leveling crosshairs
A bore sighter works just as well for making sure the cross hair is level and plumb while making it easy to sight in a new scope. Most bore sighters have a square box with smaller squares inside of it. There is a perfectly horizontal as well as verticalspace going between the smaller boxes. The only way that the verticle line of your scope's cross hair will line up with the verticle space of the bore sighter is if the scope is mounted correctly and the bore sighter is in the right spot. When I say the bore sighter is in the right spot I mean that while the arbor is in the barrel the sighter can still move counter/clockwise. Only when the sighter is in the right position and the scope is correctly mounted will the cross hair and verticle space of the bore sighter line up.
....I hope I didn't confuse you.