How big are the targets? I can see a 2ft sq steel plate at 300yds with iron sights, but not as well as i used to be able too. Gotta figure out how much magnification you need.
Off the top of my head, the leupold vx freedom line is good. I have and really like the 2-7x33
At those distances, with that round, i would highly reccomended something with moa type reticle so you can find and use your hold overs easily.