The Leupold mark AR's with Firedot are great for $400 plus. They, like the Nikon 223's are calibrated for 223/5.56mm. I have a Leupold Mark AR 1.5-4x on my AR, and a Nikon 2.5-8x in a scout mount on my Mini. Both great scopes. If you want to spend less, the Redfield Revolution is U.S. made and under $200.