Caribou are bigger than deer, but do not present as big a challenge to a game bullet as really big animals like elk and moose... I've witnessed perhaps 25-30 caribou kills with everything from 130 grain .270 bullets to 250 grainers from .338s and a 9.3 x 62, and all of the bullets worked well.. As the above posters indicated, any bullet from 140 to 175 grains that your rifle shoots accurately will work fine.... The combo that I have used the most is a .280 Rem with the 140 grain 7mm Nosler ballistic tip...

As far as shot distance goes, it might depend upon the terrain, but in most places where I have hunted caribou, the opportunity exists for some long shots if you are comfortable with them.. Personally, I'd rather take a 350 yard shot from a good steady rest than a 100 yard shot offhand or from an unsteady position...However if you don't feel comfortable with long shots, you can often close the range to 200 yards or maybe less, depending on the cover and how spooky the animals happen to be...On my last caribou hunt in Alaska, the numerous wolves and grizzlies had the caribou on edge, and they were difficult to get close to...