I do not understand boresighting scopes mounted in fixed rings. If makes sense in offset mounts or in extreme cases, but other than that.... you save 5 rounds and 5 minutes @ the range?
shoot @ 25 yds. Get on the paper, move to center..... adjust ... move to 100... that is it.
and it saves you the unpleasentness of having forgotten it in the bore and fired a live round.... there was a thread about it.