Yes they will work under good conditions and with proper shot placement. The gunsmith that built my 257 AI swore by that caliber for elk. But think of this. You spend all the money to go on an elk hunt somewhere either guided or unguided and you see a nice bull quartering away at 300 yards or so do you really want to be holding a 257 Bob? While they will work I would stick with a 30-06 with a quality 180gr bullet or larger.

The unarmed man is not only defenseless, he is also contemptible.
Niccolo Machiavelli