I've tried several on my varmint AR rig, including Burris Black Diamond, Bushnell Elite 4200 -- both of which were and are great. I ended up with a Leupold fixed 6x, though. I keep meaning to send it in to the custom shop for mildots, but it seems the best out of the box varmint AR scope I've seen. IOR has one, too, which I keep on another .223.
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