I do this: start with a LARGE piece of paper, marked with a circle (I trace the bottom of a soup can), at 25y/m.
Set rifle in rest (on bipod/bag, or whatever you use). Look down bore; line circle up in the centre of your view down the bore.
Carefully look through scope without moving rifle. Align crosshairs with centre of circle.
Get behind that gun, and aim for the centre of the circle. Once you've fired, recover the same sight picture on the centre of the circle, and carefully hold there.
Without moving the rifle, adjust the scope so the crosshairs are on the bullet impact from the ONE shot you fired.
You're now sighted for a 25y/m zero.
Move out to 100 (or whatever, but 100 is good) and carry on.
I got pretty lucky with my .243. Bolted on a set of Talley lightweights with a new scope, looked through the scope and barrel and thought it looked ok, then put the first shot dead center at 100 yards. I think the group ended up about a 1/2" to the side after 3 shots. I definitely don't always get that lucky though.
Kristian
After using my Bushnell bore sighter, I verify the bore sight by placing the rifle on a rest, removing the bolt and aligning the bore with the crosshairs at 100 yards, by looking through the barrel and the scope, and centering the bullseye in both. I then shoot my first shot at 100 yards, and it is always on one of my 16"x16" targets, which I only use for the initial sight in. However, if the first shot did not hit the target, the obvious choice would be to repeat the exercise at a closer distance. If someone is clueless enough to keep shooting, when he has no idea where the point of impact is, he deserves to waste his ammunition.
only accurate guns are interesting
I always assumed a bore sight was to get you close enough that you can use a paper target, then from there fine tuning would be required.
I once saw a fellow pull up to the range as it was starting to get dark. On a ceasefire, he headed out and put up some paper at 50yds.
He then got situated at a bench, and uncased his rifle. It didn't have a scope. It didn't have open sights either. It was a sleek, shiny stainless something or other - a Tikka or Browning I think.
He proceeded to fire a number of rounds at his target. I could hear him cursing as he plucked it from the 50y backer as I was driving away.