Re: 280 rem for elk
Welcome to LRH.
Both are capable to take down an elk on a well placed shot on those distances.
If you handload you'd have more options. However, if not, my preference would be to use the heaviest bullet (with the highest BC possible) that accurately shoots out of your rifle, i.e., Federal's .150gr NP or HSM's .162gr BTSP Interlock.
In the .140 grainers, try HSM's Trophy Gold Berger VLD or Federal's NAB.
good luck and happy safe hunting/shooting.
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