When hunting deer in dark timber:
Bushmaster 7.62x39 upper with Burris red dot.
No shots yet, but nice and light and handy.
It has the ballistics of a 30-30 to 125-150 yards and I mostly can't see past 75 yards, so I think it's the right tool for the job.
I'm right about the metric system 3/4 of the time.