I don't know who is saying a .30-06 won't work? a 220 grain bullet at or near 2,500 fps is pretty formidable. Still, some folks might desire more range.
Oh great, now we can start a minimum caliber at 100 yards and a minimum caliber at 200/300/400 yard thread.
This entire "minimum caliber" idea is a matter of personal opinion. If you are hiring a guide and he, or she ( may daughter just got her full registered guide's license), says xyz is their minimum caliber then you can be assured that they have a reason.
I can tell you from my 35 years of guiding experience that any rifle in the realm of a .270/7mm/308/30-06 with today's bullets and a competent shooter will successfully kill any bear in Alaska, at any distance from the muzzle to 300 yards.
If one can place a larger or faster bullet in the same place it might drop them a fraction of a second quicker, but it won't kill them any deader.
