Let's Revisit Boresighting

I removed the rear iron sight from a milsurp rifle this week and installed a base and scout scope. I have my own routine for boresighting, and it works great for me.  I did not have a vertical line that I could use, so I sighted on a sycamore leaf that was on the ground 50 yards out. Here is my method:

"Bore Sighting: You can get very close if you can look through the bore with the rifle in a steady position.  I cut V's in a cardboard box, and set the rifle so I can look downrange through the barrel. (Rifle is in position as if it is shouldered.) Pick out a vertical line (fencepost, tree, power pole, etc.) at 25 to 100 yards, and center it in the bore.  Turn your windage adjustment so it is on your vertical line.  Look thorugh your barrel again and make sure that your target is still centered. Now, turn the rifle on its side and line up on your mark again.  Look through your scope and adjust the elevation so it coincides.  Now, check through the barrel again and pause to think. Your elevation crosshairs will be looking downward through a straight line extending from your bore.  The bullets will be curving downward, making your hits a bit low.  Turn your elevation up a minute or two, depending on caliber and the distance to the boresighting target.  Cap your turrets and go to the range.  You will be very close."

I set up a target behind the barn at 25 yards, got a good. steady rest, and fired my first round.

Some minor adjustments and two more shots to check, and I was done.