I've used that little trick for 15 years and it has saved me a lot of ammo and cussing. I usually sight in at our local game commission range which has both high and low benchs and plenty of sandbags. I set the target at 25 yds,fire TWO shots while holding on the center of the bullseye. I then mark a heavy cross to what is the center of the two(didnt' need to do that with the 45/70). I then place the rifle solidly on the sandbags, with the crosshairs centered on the bull, and,looking throught the scope, firt move the vertical crosshair onto the cross, and then the horizontal. Then I fire one shot to verify that both barrel and scope are in alignment. Usually they are. I then move out to 50 and 100 yds, shooting either two or 3 shot groups. I occassionally have to move the vertical crosshair a little(very little), and depending on the caliber, the horizonatal. A surprising number of calibers, when sighted in at 25 yds, are "on" for a good ways out. My 45-70 is dead on with the 300's at 100 yds, and 1.5 inches high with the 400 gr FP. My 6mm(ruger #1) is 3" high at 100 and on all the way out to 275yds. Best thing is it saves time, ammo(money) and aggravation.