My thought in moving away from the 270 is that it may not be enough if the shot isn't perfectly broadside. i.e., the 30-06 or 300 would still be lethal if the elk is quartering a little. Is my thinking misguided?
Yup.
A Nosler Partition,Swift A-Frame or Barnes X from a .270 will still penetrate to the vitals and still kill the elk.
A .30 caliber will just make a bigger hole going through.
