bumpo, 500 yds aint med long, it's loooooooong for a game shot. Only an expert rifle shot should even consider such a shot and then only under ideal conditions. Butthe three calibers you mentioned, I'd only consider two of them. The 270 or the 280 and only because of ammo availability. The 270 will be on more sporting goods shelves than the 280, although the 280 has a slight preformance advantage. I n reality you should consider 300 yds a very long shot, and not one to attempt on a game animal unless you have practiced at similar ranges a lot.