a12, Years ago when I had a bighorn permit, I was faced with a similar problem.. The shots could be close or long, but in those days, range finders were not common.. So I loaded 150 Nosler BTBT's at 3400+fps.. In my old .300.. You should get 3500fps out of a good Weatherby.. Sighted in 3" high at 100, I was a tad less than 2 foot low at 500.. It was pretty simple, out to a shade over 400, hold high on the shoulder, at 500, I needed some daylight.. Worked like a charm..
I also have scopes with dots, that is an excellent way to go if, you want to go beyond 500..
