If you have a bolt this is what I do, drop the bolt then take one of those bright orange circles put it on a target or piece of cardboard and set it at 25yards. I then use a gun vise and line up my bore to centre the hole, then make my crosshairs match the dot and done. It can be done off sandbags,etc at the range on 25 or 100 yard markers. It is much easier to have a spare set of hands available to turn the adjustment knobs while you look through the scope and hold it steady, without a vise or similar to clamp the rifle down.

If your doing pumps, semi's, closed breeched Ml's than this tech will not work. I have used the Bushnell Trophy Boresighter before and it worked pretty well.