I do exactly as described above, but I just take out the bolt and use one of the most sophisticated optical instruments in God's creation, my eye. I just sight through the bore to the target, and then without disturbing the rifle I adjust the crosshairs so they match. I'm usually within 2" at 30 yards, which is good enough, and it's free.
Yip, this works just as well as any store bought bore sighter.