People here obviously have a very misguided idea about the size and build of a caribou. I have taken a bunch and watched a bunch more be shot. A mature bul caribou is about the size of a large whitetail or mule deer. Most bulls weigh about 250-275 lbs on the hoof. The other thing is they are not exactly tough to anchor. And then they are typically shot out in the open where you can watch them run if they do. Use whatever rifle you prefer out of those 3 mentioned but if it was me I would use the .308 win. Actually I have taken 2 good bulls with a .308 win and they dropped in thier tracks. There is absolutely no "need" for a .338 but if you like the round there's nothing wrong with it either, by the way I have taken them with the .338 also. The last 2 I shot were both taken with a a 7mm rem mag and Nosler Ballistic tips. If I was to buy a rifle just for caribou it would be a .270 win.