I have been on several praire dogs shoots from 1980-1988 with a 220 swift and a 22-250. Back then you had shots from 50-200 yards all day long. The longest confirmed kill was about 280 yards with a 18X scope. Shots beyond 200 yards required a spotter as the first shot was usually a miss.

However, 500 yards is really really long. You must have a awesome scope to see that far. The benchrest guys are using $2000 night force 24X for thier F-Class rigs at my range.