I LOVE Barnes 180gr TTSX in .30-06. I went to Colorado 10-21-12 hunting elk. I was a little worried about its expansion shooting long distance. I shot my first bull, a 4x5, at 530 yds. I shot him IN the shoulder. He dropped. I fired two additional shots to make sure he stayed down. Bullet went through shoulder blade, ribs, offside ribs and shoulder and out the other side. Two of Three bullets complete passthrough. Found third bullet under hide on offhand side with 3/4 expansion and weighed 170gr. I hunted at 10000 feet. I live at 3100 feet.
Less air density= Bullets Shoot further AND FLATTER. Bullets maintains speed longer= bullet is going faster when it reaches target because of ELEVATION. This is huge when using Barnes because you want to be assured of the expansion. At home (3,100 ft) at 530 yds bullet hits target at 1852 fps. At 10,000 ft bullet impacts 530 yd target at 2012 fps.