The Soviet Army method is to set the rear sight at the 100 meters setting, and sight in at 25 meters.
Once the rifle is sighted in at 25 meters, it'll be on at 100 meters.
Once sighted, setting the rear sight on the Battle Sight setting will allow body hits on a man at any range from 0 to 300 meters.
I use an "X" target.
I make these up using black tap or just printing them up on my PC printer.
Set the target at 25 meters, "about" 27 yards, and sight in on the center of the "X".
Shoot and adjust the sights until the bullets are hitting the center of the "X".
In other words the bullets are hitting exactly where the sights are aimed: The center of the "X".