I would go with the 16 inch med con barrel and a Noveske NR rail for lightweight shooter.
Rainier, Noveske, Lothar Walther and White oak all have 16 inch barrels in 1x7/1x8 that would fit your criteria, I would suggest a wylde chamber or the similar Noveske match chamber.
You will be able to hit out to 500, but you will be needing a nice clear glass.
How do you establish intent?
Well when a naked man is chasing a woman down an alley with a butcher knife and a hard on, I figure he's not collecting for the red cross...Inspector H. Callahan