A few weeks ago I wrote an article about all the trouble I was having sighting in my rifle.
I set them back to center and then went to the range, but asked for a little expert assistance. The first shot we took was almost perfect, then the 2nd wasn't. This was puzzling to both of us but we kept trying, and quickly, it seemed like we were getting close. When our adjustments stopped appearing like they were helping, we used the bore sight (which has now gone missing) and finally got to a good place, with consistency.
What helped the most?
First and foremost, a bench rest. We didn’t have a great one, but I wouldn’t recommend sighting-in without one, unless you know you have a VERY steady hand.
And to that point I must ask, how well do you know what you’re doing? I certainly didn’t, but didn't realize how little I knew until someone else, who knew more, was there watching and correcting me. If the AR is a new platform for you, would recommend getting help from the start.
The last little bit of help came from my boresight. A magnetic red laser that one sticks on the muzzle of the rifle. Not only can this almost never be used outside, but it really needs to be used with two people, one handling the gun and one spotting. This little device, though now lost :( cost me less than $30, but saved me another marathon at the range, trying to get things right. When you install the bore sight, be sure there is no live ammo in your gun and you have locked back the bolt.