Is a basic sp the only ammo you can to use. I would tend to use a bonded bullet on a trip like that and then it would be what 150 or 165 it likes best assuming weight is 400 to 800lbs. Accubond , swift sciroco, rem core-lokt ultra bonded, hornady interbond. They all well work real well. If your takeing ammo try a couple . If your buying there see what you can get. All will work well.
I saw on "Choose Your Weapon" on the Outdoor channel the other night one of the guys picked a .308 and a 150 gr. bullet for Caribou. To me the bullet seemed kind of light for a big animal like that. He proved me wrong.
A strong jacket is what you're looking for to get the round all the way into teh boiler room and shut that animal down. .308 short action rifles make trekking through the mountains a lot more pleasant than hauling a big magnum rifle. Stalking in close will be another consideration.
Folks still use bows on this size animal so a .308 with the right load and shot placement ought to be plenty big medicine for the job.