Red dots for AR's are not a true accuracy item. They are ment to aquire your close in (read 100yds or less) quickly and be able to put multiple shots on target quickly. They also work well for shooting moving targets. Remember that you do not close one eye with red dots, you shoot with both eyes open to keep your peripheral vision to aquire other threats/targets. As far as accuracy is concerned; you should be able to keep them inside 4" or so at 100 yds depending on how fast you are shooting.

Have fun with it, they are a blast once you get the nack of keeping both eyes open.