Originally Posted by
Potashminer
It has been my practice for a number of years to always start with a new-to-me rifle and scope at 25 yards. You can peer down the bore at home (if you can remove the bolt) and get the crosshairs on the same point, but I like to start at 25 yards with at least 2 foot x 2 foot cardboard with a vertical line and a horizontal line. Aim for the intersection and fire pairs - you should get two bullet holes very close or overlapping. Then adjust scope turrets and repeat - walk your pairs of holes until they are exactly on the vertical line, and dead on or a bit low of the horizontal line. At that point, ready to move a target to 100 yard line and sight in as you wish. Many people will call 2" high at 100 yards "good enough" for hunting.
Many rifles change the point of impact as the bore fouls or the barrel warms up. You need to discover what your rifle does. So, start with a clean cold barrel, on another day's session. Mark or note the order of the bullet holes, to see if a drift occurs as you fire 5 rounds. If you are going to go hunting with a clean cold bore, that is what you need sighted in for. A "clean cold bore" is a once a day shot, so "sighting in" can involve many trips to your shooting place. And then you want to know if your rifle will start to drift as the barrel fouls, or as it heats up. If your first shot did not do the job, you are rapidly getting into an undesirable situation - your game may be wounded, likely moving, if not running, and it has become much more difficult to put it down. So, put all your marbles on that first shot - know where it goes.