5.56 is definately adaquate for yotes, we shot to 600 accurate in the army, and even further with FA. We only had 3.5X optics too
As for the Mini-14 you might be hard pressed that far away. My dad had a laminate, target and it was good, but not that good. He was always outperformed by a bolt. you wouldn't think an AR is that much more accurate but they are
