300 win mag, 180gr E tip at 300 yards. One of the guys I was with used the same ammo at 350 yards, the other used a 140gr AccuBond in a 7mm Rem Mag at 500 yards. We didn't look for longer shots, but each group of caribou was moving away from us when we got in range. All dropped with 1 shot, although I put a second in mine when he kicked a bit. He was right by water and I wanted him down on the bank.