If you sight in at 25 feet you will be really high at 100 yards. The offset between the bore and scope on an AR is roughly 3 inches. If you sight in at 25 feet, I would expect you to be 2 1/2 or 3 feet high at 100 yards.
One way to sight in a AR is to take the upper off and remove the bolt. Now place the upper on a steady rest of some type. Find something to aim at 100 yards, maybe a pie plate. Now look down the bore and adjust the upper until the target is centered in the bore. Now adjust the scope until the crosshairs are on the target, keeping the target centered in the bore as well. You can use the same technique with a bolt gun with the bolt removed. I can usually get within 3" or 4" at 100 yards without firing a shot.
Forget boresighting(unless you are using a bolt gun),and place a target a 25 yds..........take a couple of shots,and adjust your scope to hit dead center(Remember this....if your scope is a 1/4" per click at 100 you'll have to use 4 clicks at 25 yds to move your shot group 1/4" at 25 yds).Your shots should be approximately 1" high at 50yds,and 2" high at 100.
Make minor adjustments(right,left ect.)at 100 until you have it where you want it,and you'll be good to go with very few shots expended.
Put up a target at close range. Shoot a few shots to see where it is hitting. Adjust the windage first, that's the left, right point of impact. When it is hitting the center line you can the adjust the elevation. HMB