Well one scenario is that your sights are waaaay off from messing with them too much. Try this:
Remove the upper from the rifle and clap it down somehow, either in a vise or use some other way to secure it down so it doesn't move. Next loosen the vise and aline the bore on a verticle taget, 50-100 meters away, then center the taget in the bore from 12 o'clock to 6 o'clock, the front sight post should be on line and verticle with the target.
Now tighten the vise. Then adjust the rear sight windage untill you get a proper sight picture on the vertical target throught the bore. If you did it correctly the rear sight aperature will be in the center of the front sight post when the barrel is properly alined in the reciever.
if the barrel isn't alligned in the sights, usually excessive windage is present and the worst case will be that you need to replace the upper reciever.
You can also try to shoot 3 rounds at a target 20 feet away, if you can hit it, move it back 10 feet, untill you reach 100 meters. if for somereason your shot groups start to wander left or right, then you have a major windage, barrel or reciever problem. At this point youre better off going to a AR gunsmith and have them look at it.
The Cheat